----In recent years problem of global warming has become very serious. ----That’s right.

问题补充：

----In recent years, problem of global warming has become very serious.

----That’s right. People are facing diversity of natural disasters now.

A. /, a

B. a, the

C. the, a

D. a, a

答案：

A. /, a

B. a, the

(答案→)C. the, a

D. a, a

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