It ______ 12 rabbits to test a sample of vaccine, now it takes only 6.

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It ______ 12 rabbits to test a sample of vaccine, now it takes only 6.

A. used to taking

B. used to take

C. is used to take

D. was used to

参考答案:

B答案为B。过去曾经需要12 个兔子测试疫苗样本,现在只需要6 个。used to do “曾经”; be used to doing sth.“习惯于做某事”。