It’s generally agreed that the greatest threat facing the world today is the warming of the earth’s atmosphere, commonly called global warming or the greenhouse effect. But what is the cause of the greenhouse effect
We have been producing too many of the gases which, when they are released into the earth’s atmosphere, trap heat, and thus raise their temperatures. There are several gases involved, but the main ones are carbon dioxide (二氧化碳) and chlorofluorocarbons (氯氟甲烷)--often called CFCs. The carbon dioxide comes from burning forests and from bunting fossil fuels such as oil and coal. The CFCs are given off by refrigerators and air-conditioning systems. Carbon dioxide is to blame for 56% of the greenhouse effect, and CFCs for 23%.
The global warming we are experiencing now is only a result of the carbon dioxide and other gases we have dumped into the atmosphere up to the 1960s. In other words, the damage may have already been done. Tempe
A. Cause and Effect of Global Warming
B. Damages Done by Global Warming
C. Global Warming and Industrial Development
D. Solution to the Problem of Pollution
In the last ten years, the Internet has opened up incredible amounts of information to ordinary citizens. But using the Internet can be like walking into a library where the books are all lying on the floor in piles. While tools like Google allow some structured search, much of the data from such searches is outdated or of questionable value. Some web enthusiasts have taken up the task of organizing information through a democratic means that only the Internet allows: an encyclopedia of the people, by the people, and completely free to copy and distribute.
This people’s encyclopedia’ of the Web (a free site called Wikipedia) has provided a unique solution by inviting individuals to participate in the process of rationalizing and updating web con- tent. At the heart of this movement are wikis, web sites that allow users to directly edit any web page with one click of the mouse.
Wikipedia (the largest example of these collaborative efforts) is a function
A. give up.
B. be aborted.
C. reduce.
D. sink.
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