单项选择题

The reason why all the solar energy falling on the earth can' t be utilized is that （）.

A．only a very small part is available
B．the sun is too distant from the earth
C．it takes thousands of years for this energy to be stored up in coal and oil
D．our scientific knowledge is not sufficient

<上一题目录下一题>

热门试题

单项选择题

In order to support this argument, the writer gives the example that （）

A．a machine using solar energy efficiently has already been developed
B．the sun is our final source of power
C．man uses only a tiny part of the sun's energy
D．the part of the sun's energy we use is used indirectly

单项选择题

Why can't astronauts drink water from cups（）

A．The water would come from the open cups.
B．The water would spill all over their food
C．Crams would float in the cups
D．The cups would float in the air.