About gene-targeting drugs are already in testing pipeline. It won’t be long they are put into effect.
A. two dozen; before
B. two dozens; that
C. two dozens of; before
D. dozens; that
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(答案→)A. two dozen; before
B. two dozens; that
C. two dozens of; before
D. dozens; that
解析：考查数词及连词。dozen前加数词，后不可加of；it be … before …在……之前有一段时间。根据句意选A。