单项选择题

How did people begin to use fire（）

A．Not everybody knows how people began to use fire.
B．Nobody knows how to make a fire.
C．It is an Australian who started a fire.
D．We are not sure how people began to use fir

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单项选择题

Vitamins do not provide energy, nor do they construct or build any part of the body. They are needed for ______ foods into energy and body maintenance.

A. transforming
B. transferring
C. altering
D. shifting

单项选择题

What two problems can man solve by burning garbage（）

A．The shortage of energy and air pollution.
B．The shortage of energy and the land to hold garbage.
C．Air pollution and the shortage of fossil fuel.
D．Air pollution and the shortage of land to hold garbag