Experiment of this kind _____ in both the U.S. and Europe well before the Second World War.

A. have conducted
B. have been conducted
C. had conducted
D. had been conducted
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科目：高中英語 來源：北京高考真題 題型：單選題

Experiment of this kind _____ in both the U.S. and Europe well before the Second World War.
[     ]
A. have conducted
B. have been conducted
C. had conducted
D. had been conducted

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科目：高中英語 來源： 題型：

Experiment of this kind________in both the U．S. and Europe well before the Second World War.

A. have conducted  B. have been conducted

C. had conducted  D. had been conducted

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