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Ateamofscientists

練習題2.64W

問題詳情:

Ateamofscientists

A team of scientists _____ the effects of acid rain over the last twenty﹣year period.(  )

A.studied  B.had studied

C.is studying   D.has been studying

【回答】

D

知識點:動詞時態與語態

題型:選擇題