It is believed that a new kind of drug ______ by the scientists and they are hopeful that they will succeed in a few months.

A. has been developed                  B. is being developed 

C. is developing                       D. has developed

It is believed that a new kind of drug ______ by the scientists and they are hopeful that they will succeed in a few months.

1. A.
   has been developed
2. B.
   is being developed
3. C.
   is developing
4. D.
   has developed

It is believed that a new kind of drug ______ by the scientists and they are hopeful that they will succeed in a few months.