Over the past three decades the number of students leaving home each year to study abroad ________ at an annual rate of 3.9 percent, from 800,000 in 1975 to 3.5 million in 2008．

1. A.
   grew
2. B.
   grows
3. C.
   have grown
4. D.
   has grown

Over the past three decades the number of students leaving home each year to study abroad ____________ at an annual rate of 3. 9 percent, from 800, 000 in 1975 to 3. 5 million in 2008.

A. grew                 B. grows                      C. have grown                     D. has grown