题目内容

The Chinese government _____ research into vaccine against H1N1for months, recently many have received
the first doses.

A. is doing
B. has done
C. had been doing
D. did

试题答案

C
相关题目
The Chinese government _____ research into vaccine against H1N1for months, recently many have received
the first doses.
[     ]
A. is doing
B. has done
C. had been doing
D. did
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