地球人口剧增，下列哪些现象可能会发生 （1）空气清新（2）资源消耗增多（3）环境

过正方体外接球球心的截面截正方体所得图形可能为        （填序号）①三角形 ②正方形 ③梯形 ④五边形 ⑤六边形

GPS表示的是______，它可以为飞机、轮船、汽车等______．

Electric cars will not be really much cleaner than autos powered by mineral fuels until they rely less on electricity produced from usual coal-fired power plants.

“For electric vehicles to become a major green alternative, the power fuel has to move away from

coal, or cleaner coal technologies have to be developed,” said Jared Cohon, the chairman of a National

Research Council report released on Monday. About half of US power is produced by

burning coal, which gives off many times more of traditional pollutants than natural gas, and about

twice as much of the main greenhouse gas carbon dioxide. Nuclear and renewable power have to

generate a larger portion of US power for electric cars to become much greener compared to

gasoline-powered cars, Cohan, who is president of Carnegie Mellon University, said in an interview.

Advances in coal burning, like capturing carbon at power plants for permanent burial underground,

could also help electric cars become a cleaner alternative to vehicles powered by fossil fuels, he said.

Pollution from energy sources did $120 billion worth of damage to human health, agriculture and

recreation in 2008, and electricity was responsible for more than half of the damage, said the NRC

report.

Electric cars have their benefits such as reducing imports of foreign oil. But they also have hidden

costs. Materials in electric car batteries are hard to produce, which adds to the energy it takes to make

them. In fact, the health and environmental costs of making electric cars can be 20 percent greater

than usual cars, the report said.

The report estimated that electric cars could still cost more than gas-powered cars to operate and

manufacture in 2030 unless US power production becomes cleaner.

1. Why are electric cars not clean enough?

A. Because they run too slowly              B. Because they are too expensive

C. Because they rely on coal-fired power.      D. Because they give off more carbon dioxide.

2. We can infer from the passage that ______.

A. electric cars will soon take the place of gas-powered cars

B. no one holds hope for electric cars at present

C. electric cars waste more energy than before

D. some people believe that electric cars are cleaner

3. The underlined word “them” refers to “______”.

A. electric cars     B. batteries       C. producers        D. materials

4. Which of the following is NOT mentioned as a way to make electric cars cleaner?

A. Developing cleaner coal technologies.        B. Making electric cars run faster.

C. Generating more unclear power.             D. Making advances in coal burning.

简述肉毒梭菌的致病机制。

这些蔬菜长得好的原因，是农民精心管理的结果。