单项选择题

What is the main idea of the passage

A．Coal-fired plants are an important source of electricity in the United States and are likely to remain so.
B．Generating electricity from coal is comparatively recent in the United States.
C．Coal is a more economical fuel than either oil of nuclear power.
D．Coal is a safer and more dependable fossil fuel than oil or gas.

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单项选择题

In the author's opinion, the importance of coal-generated electricity could increase in the future for which of the following reasons

A．The possible substitutes are too dangerous.
B．The cost of changing to other fuels is too great.
C．The future availability of other fuels is uncertain.
D．Other fuels present too many environmental problems.

单项选择题

What makes coal-fired power plants less attractive today

A．Acid rain.
B．Problems of waste disposal and pollution control.
C．Future growth of nuclear power.
D．Sufficient supply of oil and natural gas.