第3部分：概括大意与完成句子(第23～30题，每题1分，共8分)
下面的短文后有2项测试任务：
(1)第23～26题要求从所给的6个选项中为第2-5段每段选择1个最佳标题；
(2)第27～30题要求从所给的6个选项中为每个句子确定1个最佳选项。
Natural Gas
1 Natural gas is produced from reservoirs deep beneath the earth's surface．It is a fossil fuel
(矿物质燃料)，meaning that it is derived from organic material buried in the earth millions of yearsago．The main component of natural gas is methane(甲烷)．
2 The popularity and use of clean natural gas has increased dramatically over the past 50 years as pipeline infrastructure(基础设施)has been installed to deliver it conveniently and economically to millions of residential，commercial and industrial customers worldwide．Today，natural gas serviceis available in all 50 states in the U．S．，and is the leading energy choice for fueling Americanhomes and idustries。More than 65 million American homes use natural gas．In fact，natural gas
www.med126.comisthe most economical source for home energy needs，costing one-third as much as electricity．In addi-tion to heating homes，much of the gas used in the United States is used as a raw material to manu-facture a wide variety of products，from paint，to fibers for clothing，to plastics for heahhcare，con-puting and furnishings．Natural gas is also used in a significant number of new electricity-generating power plants．
3 Natural gas is one of the safest and cleanest fuels available．It emits less pollution than oth-er fossil fuel sources．When natural gas is burned，it produces mostly carbon dioxide(
二氧化碳) and water vapor-the same substances emitted when humans exhale．Compared with some other fos-sil fuels，natural gas emits the least amount of carbon dioxide into the air when combusted(燃烧)， making natural gas the cleanest burning fossil fuel of a11．
4 The United States consumes about one-third of the world'S natural gas output，making it the largest gas-consuming region in the world．The U．S．Department of Energy'S Energy Information Ad-ministration forecasts that natural gas demand will grow by more than 50 percent by 2025．
5 There are huge reserves of natural gas beneath the earth's surface．The largest reserves of natural gas can be found in Russia，West and North Africa and the Middle East．LNG(液化天然气)has been produced domestically and imported in the United States for more than four decades．
Today，the leading importes of LNG are Japan，Korea，France and Spain．
23．Paragraph 2_________．
24．Paragraph 3________．
25．Paragraph 4_________.
26．Paragraph 5________．
A．Popularity and use of natural gas
B．Natural gas reserves and supply
C．Natural gas prices
D．Clean fuel of choice
E．Disadvantages of natural gas
F．Natural gas consumption
27．Natural gas is stored deep________．
28．Natural gas is recognized as the most economical energy source_________．
29．When manufacturing many products，people commonly use natural gas____________．
30．It is estimated that by 2025 that natural gas demand in the United States will increase_________．
A．over the past 50 years
B．beneath the earth surface
C．by more than 50 percent
D．for more than four decades
E．as a raw material
F．for home energy needs
第4部分：阅读理解(第3l～45题，每题3分，共45分)
下面有3篇短文，每篇短文后有5道题。请根据短文内容,为每题确定1个最佳选项。
第一篇
How the First Stars in the Universe Came into Existence
How the first stars formed from this dust and gas has been a burning question for years，but a state-of-the-art computer simulation now offers the most detailed picture yet of how these first stars in the universe came into existence，researchers say．
The composition of the early universe was quite different from that of today，and the physics that governed the early universe were also somewhat simpler．Dr．Naoki Yoshida and colleagues in Japan and the U．S．incorporated these conditions of the early universe，sometimes referred to as the "cosmic dark ages，"to simulate the formation of an astronomical object that would eventually shine its light into this darkness．
The result is a detailed description of the formation of a protostar-the early stage of a massive primordial star of our universe，and the researchers'computer simulation，which has been called a "cosmic Rosetta Stone．"sets the bar for further investigation into the star formation process．The question of how the first stars evolved is so important because their formations and eventual explo-sions provided the seeds for subsequent stars to come into being．
According to their simulation，gravity acted on minute density variations in matter，gases，and the mysterious"dark matter''of the universe after the Big Bang in order to form this early stage of a star-a protostar with a mass of just one percent of our sun．The simulation reveals how pre-stellar gases would have actually evolved under the simpler physics of the early universe to form this protostar．
Dr．Yoshida's simulation also shows that the protostar would likely evolve into a massive star capableof synthesizing heavy elements，not just in later generations of stars，but soon after the Big Bang．
"This geneal picture of star formation，and the ability to compare how stellar objects form in different time periods and regions of the universe，will eventually allow investigation into the originsof life and planets，"said Lars Hernquist，a Professor of Astronomy at Harvard University and a coauthor of this latest report．"The abundance of elements in the universe has increased as stars haveaccumulated，"he says，"and the formation and destruction of stars continues to spread these ele． ments further across the universe．So when you think about it．a11 of the elements in our bodies originally formed from nuclear reactions in the centers of stars，long ago．"
Their simulation of the birth of a protostar in the early universe signifies a key step toward theambitious goal of piecing together the formation of an entire primordial star and of predicting the massand properties of these first stars of the universe．More powerful computers，more physical data，andan even larger range will be needed for further calculations and simulations，but these researchers hope to eventually extend this simulation to the point of nuclear reaction in．itiation-when a stellar ob． ject becomes a true star．
"Dr．Yoshida has taken the study of primordial star formation to a new level with this simulation，but it still gets us only to the halfway point towards our final goal．It is like laying the foundation of a skyscraper，"said Volker Bromm，Assistant Professor of Astronomy at the University of Tex． as，Austin and the author of a companion article．"We must continue our studies in this area to un-derstand how the initially tiny protostar grows，layer by layer，to eventually form a massive star．Buthere，the physics become much more complicated and even more computational resources are needed．"
31．According to the first two paragraphs，the early universe_______．
A．was governed by simpler physics
B．got fewer stars shinning in it
C．started over 13 billion years ago
D．was composed in a way similar to that of today
32．What can the state-of-the．art computer simulation tell us about?
A．How the Big Bang occurred about 13 billion years ago．
B．How"cosmic dark ages"came into existence．
C．How dust grains and gases were formed after the Big Bang．
D．How the first stars canle into being after the Big Bang．
33．What does the"astronomical object"in paragraph 2 refer to?
A．cosmic dark ages．
B．dust grains and gases．
C．a protostar．
D．the early universe．
34．According to paragraph 4，what is NOT true about a protostar?
A．It developed into a massive star during the Big Bang．
B．It evolved from pre-stellar gases．
C．It was able to integrate heavy elements when evolving into a massive star．
D．It had a mass of one percent of the sun．
35．According to the last paragraph，all of the following are goals of the simulation project EXCEPT
A．to know more about the mass and properties of the first stars of the universe
B．to simulate the process of how the early universe began
C．to apply the simulation to the study of nuclear reaction initiation
D．to discover the truth about the formation of a protostar
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