Experience of this kind in both the U.S. and Europe well before the Second World War.A. ha

发布时间：2020-08-16 17:56:16

Experience 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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A. have conducted
B. have been conducted
C. had conducted
(答案→)D. had been conducted
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