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【单选题】

If the balance of nature is ____ , a series of problems will arise .

A.
disturbed
B.
troubled
C.
interrupted
D.
confused
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参考答案:
参考解析:
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举一反三

【单选题】Madame Curie is believed _______ radium.

A.
discovering
B.
having discovered
C.
to have discovered
D.
to discover