He picked up an envelope 50 dollars in it.
A. containing
B. contained
C. which contains
D. which was contained
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(答案→)A. containing
B. contained
C. which contains
D. which was contained
解析：考查现在分词做定语，envelope和contain是主动关系，句意是：他捡起一个里面有50美元的信封。C项应该是过去时，选A。