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

1. A.
   is doing
2. B.
   has done
3. C.
   had been doing
4. D.
   did

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