Watching the online open courses of some famous European and American universities _______a new fashion among white collars in China over the past few months.

A. became           B. had become           C. has become       D. becomes

Watching the online open courses of some famous European and American universities _______a new fashion among white collars in China over the past few months.

1. A.
   became
2. B.
   had become
3. C.
   has become
4. D.
   becomes

Watching the online open courses of some famous European and American universities _______a new fashion among white collars in China over the past few months.

A. became           B. had become           C. has become       D. becomes

Watching the online open courses of some famous European and American universities _______a new fashion among white collars in China over the past few months.