单项选择题

As there is less and less coal and oil, scientists are exploring new ways of making use of （）energy, such as sunlight, wind and water for power and fuel.

A. primary
B. alternative
C. instant
D. unique

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单项选择题
Some of you may have finished unit one.（）, you can go on to unit two.

A. If you may
B. If you do
C. If not
D. If so
单项选择题
Children need friends（）their own age to play with.

A. of
B. for
C. in
D. at
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