题目内容
The Chinese government ______ research into vaccine against H1N1for months, recently many have received the first doses.
has done B. did C. was doing D. had been doing did
D
解析:
略
练习册系列答案
相关题目
题目内容
The Chinese government ______ research into vaccine against H1N1for months, recently many have received the first doses.
has done B. did C. was doing D. had been doing did
D
略