1、雅思（阅读）模拟试卷 30及答案与解析 一、 Reading Module (60 minutes) 0 THE LIFE CYCLE OF A STAR It has been conservatively estimated that there are some 10,000 billion, billion stars in the universe. It is difficult to know the exact age of a star (astronomers have identified stars as young as 25,000 years old and ot
2、hers are thought to be over 10 billion years old), but what astronomers do know is that there are many different kinds. How each star is formed, and its mass, influences its type and longevity. A star is born in a nebula, which is a giant cloud of gas and dust. The larger the amount of matter that i
3、s in the nebula, the greater the mass of the star that is created. Inside these nebulae are dense areas of gas, which, due to their density, have a stronger gravitational pull than the rest of the nebula. Gradually, gravity drags the gas in the nebula together and it begins to spin and become increa
4、singly hotter. Once the temperature reaches 15,000,000 , nuclear fusion occurs in the centre of the cloud, and it begins to glow brightly. It stabilizes at this temperature, contracts slightly and becomes what is known as a main sequence star (an example of this is our own Sun). It can remain in thi
5、s stage for millions or billions of years. As it glows, hydrogen in the centre (through the nuclear fusion) becomes helium. Eventually the hydrogen supply in the core diminishes and the core of the star becomes unstable, contracting more. However, the outer parts of the star (which are still mainly
6、hydrogen) expand and cool, and in doing so, the star starts to glow red. It is at this stage that the star becomes a red giant. It is anticipated that it will take the Sun another 5 billion years to reach this stage. By then it will have grown large enough to engulf the three closest planets Mercury
7、, Venus and Earth) and glow 2,000 times brighter than it currently does. Exactly how a star will react in the red giant phase depends on its mass. Throughout the red giant phase, the hydrogen in the outer parts carries on burning, and the centre gets hotter and hotter. On reaching 200,000,000 , the
8、helium atoms fuse forming carbon atoms. The remainder of the hydrogen explodes and forms a ring around the core called a planetary nebula. With medium-sized stars, once the final helium atoms have fused into carbon atoms, the star starts to die. The gravitational pull leads to the last of the stars
9、matter collapsing inwards and compacting to become extremely dense. A star like this is called a white dwarf. It will shine white-hot until the remaining energy (thermal energy trapped in its interior) has been exhausted after which it will no longer emit light. This can take in excess of several bi
10、llion years. It is then termed a black dwarf (a cold, dark star, perhaps replete with diamonds) and remains in that stage forever. When the larger red giants (massive stars) collapse, which happens in an instant, so much planetary nebula is created that this gas and dust can be used as building mate
11、rial for planets in developing solar systems. In addition, with massive stars, as the temperature increases, the carbon atoms get pulled together to form increasingly heavier elements like oxygen, nitrogen and finally iron. Once this happens, fusion ceases and the iron atoms begin absorbing energy.
12、At some point in the future, this energy is released in a huge explosion called a supernova. A supernova can have a core temperature of up to 1,000,000,000 and the explosion can light up the sky for weeks, outshining an entire galaxy. Astronomers believe that Earth is made up of elements formed from
13、 the inside of stars, in particular red giants that exploded as supernovas. These massive stars have an average life span of one million years. After becoming a supernova, the remaining core of a massive star that is 1.5 to 4 times as massive as the Sun becomes a neutron star. It starts to spin and
14、often emits radio waves. If these waves occur in pulses, the neutron star is referred to as a pulsar. When a massive star has eight or more times the mass of the Sun, it will remain massive after the supernova. It has no nuclear fusion supporting the core and becomes engulfed by its own gravity. Thi
15、s results in a black hole, which sucks in any matter or energy that passes close to it. The gravitational field of a black hole is powerful enough to prevent the escape of light and is so dense that it cannot be measured. The phrase black hole originated from the physicist John Archibald Wheeler; be
16、fore this, black holes were known as frozen stars. Wheeler came up with this name two years before the proof of the existence of the first black hole, X-ray binary star Cygnus X-1, in 1971. Astronomers think that there may be a black hole at the centre of each galaxy. The life cycle of a star is rea
17、lly that-the materials from an exploded star mix with the hydrogen of the universe. This mixture in turn will be the starting point of the next star. The Sun is a case in point, containing the debris from numerous other stars that exploded long before the Sun was born. 1 Questions 1-6 Different stag
18、es and types of stars are mentioned in Reading Passage 1. Choose ONE of the types or stages (A-H) from the box below which best matches the descriptions (Questions 1-6). Write your answers in boxes 1-6 on your Answer Sheet. NOTE: you may use any answer more than once. A nebula B main sequence star C
19、 red giant D white dwarf E black dwarf F supernova G neutron star H black hole the Sun _ 2 birthplace of a star _ 3 a dying star _ 4 sometimes has pulsating waves _ 5 its size is immeasurable _ 6 its supply of energy has run out _ 7 Complete the sentences using NO MORE THAN THREE WORDS for each answ
20、er. Write your answers in boxes 7-13 on your Answer Sheet. Hydrogen will turn to helium after _ occurs. 8 The colour of the red giant is formed as the _ becomes smaller and the outer areas cool. 9 At 200,000,000 the stars helium atoms fuse into carbon atoms, and then the star 10 Unlike small and med
21、ium-sized stars, large stars _ quickly. 11 A black holes _ stops light from being emitted. 12 Astronomers knew about _ before they were able to confirm their existence. 13 Planets and stars are likely to consist of _ from exploded celestial bodies. 13 TOMATO RIPENING Tomatoes give off minute quantit
22、ies of ethylene gas which is active in starting the natural ripening process. If left to nature, however, the tomatoes ripen in a random way. The trickled ethylene gas process of tomato ripening consists of exposing the tomatoes to a low concentration of ethylene gas under controlled temperature con
23、ditions in a special tomato-ripening room. This treatment initiates and controls the speed of the natural ripening and colouring process in the tomatoes. Controlled ripening and colouring enables the grower to market tomatoes of more uniform colour and quality than is possible with green or field-ri
24、pened produce. Timing of harvesting and marketing may, within limits, also be regulated by the use of controlled ripening and colouring in order to achieve maximum returns and make the best use of labour and equipment. Ripening Conditions All fruit must be mature green at harvest for controlled ripe
25、ning to be successfully carried out. Relative humidity does not appear to be of great importance in the tomato-ripening process. Little moisture loss from the tomatoes occurs during the ripening process due to the relatively impermeable nature of the tomato skin. Ripening time will depend on the rip
26、ening temperature range; however, ripening temperatures above 24 will result in poor colour development with yellow or orange fruit rather than red. The heating and cooling capacity should be such that the tomatoes can be brought to the recommended ripening temperature within 24 hours. General Arran
27、gement A typical arrangement for a tomato ripening room is shown in Figure 1 with the essential components of the system identified. Room Size and Construction For efficiency and convenience in operation, on-farm tomato ripening rooms are usually sized to accommodate the normal daily tomato pick dur
28、ing the peak harvest time. The room capacity is generally in the range of two to ten tonnes of tomatoes; however, larger rooms may sometimes be installed. Since the average ripening time is three or four days, the provision of multiple rooms on the one farm is generally desirable. Air Circulation an
29、d Ventilation System Fan-forced air circulation is required for adequate and uniform temperature control and ethylene gas distribution in the ripening room. An air circulation rate of two-room air volumes per minute is recommended for good results. This is equivalent to around 480 cubic metres of ai
30、r per hour per tonne of tomatoes. At the recommended heating or cooling capacity of 0.6 to 1.2kw per tonne of tomatoes, this gives an air temperature differential of 3.5 to 7 across the heating or cooling system. These high air circulation rates are necessary to limit variations in temperature in di
31、fferent parts of the room to acceptable levels and to achieve an adequate rate of heating or cooling of the tomatoes. The ventilation system circulates the room air continuously, introducing a small proportion of fresh air and exhausting a similar amount of air at the same time. This prevents a buil
32、d up of ethylene gas in the room and also removes carbon dioxide produced by the fruit during respiration. If this carbon dioxide were allowed to build up to too high a level in the room atmosphere, it would interfere with the ripening process. Temperature Control System The temperature of tomatoes
33、in the ripening room has a great influence on the ripening process. In fact, the product heat load usually represents around 80% of the total heat load. The remainder is due to heat transmission through the external walls of the room and the fresh air exchange rate. In some cases, both heating and c
34、ooling are required to maintain the room temperature within the required range. The time required for ripening can be reduced to some extent by increasing the temperature. Reverse cycle air-conditioners are successfully used for both heating and cooling in tomato-ripening rooms where humidity contro
35、l does not appear to be of great importance. Supply and Control Systems With the trickled ethylene gas system, a low concentration of ethylene gas is maintained in the ripening room atmosphere by a continuous small, controlled flow of gas of about 10 parts per million (ppm). Ethylene gas is supplied
36、 as bottled gas under high pressure and it is released into the ripening room through a pressure regulator and metering system. The outlet gas pressure is adjusted by means of the gas pressure regulator and the gas flow rate is then adjusted by the fine needle valve. A normally closed solenoid valve
37、 in the ethylene gas supply line ensures that gas is not discharged into the room unless the fans and ventilation system in the ripening room are operating. The solenoid valve is electrically interlocked with the operation of the ventilation system fans and is also controlled by an air flow switch.
38、A gas control thermostat is used to measure when gas should be supplied to the room. The temperature-sensing element of this thermostat is pushed into a tomato so that it senses the pulp temperature of the tomatoes in different parts of the room. Provided that the ethylene gas supply and control sys
39、tems are correctly arranged, the ethylene gas concentration in the room will not exceed the low level which is sufficient for ripening but is far below the explosion hazard level. Under these conditions, tomato-ripening rooms installed on farms and used only for ripening fruit produced by the owner
40、have been approved by certain Electricity Commissions as not constituting a hazardous location. (Adapted from an article written by Brian Hesse for the Electrofarming Notebook for The South East Queensland Electricity Board, October 1989.) 14 Complete the sentences in the box below. Use NO MORE THAN
41、 THREE WORDS OR A NUMBER for each answer. Write your answers in boxes 14-16 on your Answer Sheet. Requirements for successful use of the Ethylene Gas System for Tomato Ripening: Tomatoes should be picked when they are _. 15 Room temperature must be _ . 16 Optimal ripening temperature for fruit must
42、be achieved _ . 17 Complete the flow chart below using in formation from the text. Use NO MORE THAN THREE WORDS for each answer. Write your answers in boxes 17-20 on your Answer Sheet. 21 Below is a list of assumptions. Using the information given in the passage, choose: TRUE if it is a reasonable a
43、ssumption FALSE if it is NOT a reasonable assumption NOT GIVEN if it is not possible to make the assumption from the information in the text. Write your answers in boxes 21-27 on your Answer Sheet. Carbon dioxide is not beneficial to the ripening process. _ 22 The outside air temperature determines
44、the amount of extra heating needed in the ripening room. _ 23 Increased temperature can speed up the maturing process. _ 24 For successful tomato ripening, humidity levels need to be carefully monitored. _ 25 The solenoid valve has to be checked at regular intervals. _ 26 A build up of ethylene gas
45、may result in an explosion. _ 27 Setting up ethylene gas ripening rooms is not always safe. _ 27 ECO-TOURISM If you still believe the once-commonly held misconception that tourism is only an indulgence for the wealthy, you are out of step with the times! The tourism market is accessible to, and inde
46、ed marketed toward, many different sections of the community. Adventurers, fitness freaks, nature-lovers and business people all contribute to a rapidly expanding sector of the global economy. Section A This billion-dollar industry, whilst affected slightly by the unforeseen events of 11 September 2
47、001, has experienced significant growth since the late 1980s. The subsequent economic benefits for governments are well-documented as tourism boosts foreign investment and foreign exchange. Large-scale resorts and civil infrastructure were often the only response to successful marketing and increase
48、d tourist demand. It is not surprising then that the direct impact on the environment and regional or indigenous populations became a contentious issue. Governments and big business became the target of environmentalists and activists who argued that mass tourism was not (and is not) sustainable. As
49、 hordes of tourists descended on often overcrowded beaches and overused parklands, this became apparent. Eco-tourism was born. Section B The broad concept of eco-tourism as a nature-based, culturally sensitive form of tourism was taken up enthusiastically because there appeared to be few losers. Governments were given a convenient escape route as eco-tourism appeased the environmentalists and local communities, but still provided income.
