问题

Scientists warn us _____ the need tokeep an eye ____ the greenhouse effect.
A:to; in
B:of; to
C:in; on
D:of; on
B:of; to
C:in; on
D:of; on
正确答案是:
同类题型
I like exercise such as _____ sports.
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I’ll make some sandwiches, just ________ we get hungry later