下面的短文後有2項測試任務：
(1)第23～26題要求從所給的6個選項中爲第2-5段每段選擇1個最佳標題；
(2)第27～30題要求從所給的6個選項中爲每個句子確定1個最佳選項。
Natural Gas
1 Natural gas is produced from reservoirs deep beneath the earth's surface．It is a fossil fuel
(礦物質燃料)，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(基礎設施)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 isthe 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(燃燒)， 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(液化天然氣)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．
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