.Because of the sharp drop of birth rate, the number of students sitting the college entrance exams ______ all the time

1. A.
   is declining
2. B.
   has declined
3. C.
   have been declined
4. D.
   were declining

.

 Because of the sharp drop of birth rate, the number of students sitting the college entrance exams ______ all the time

       A. is declining              B. has declined      

       C. have been declined    D. were declining

Because of the sharp drop of birth rate, the number of students sitting the college entrance exams ______ all the time

       A. is declining              B. has declined      

       C. have been declined    D. were declining

.
Because of the sharp drop of birth rate, the number of students sitting the college entrance exams ______ all the time