We ________ in this modern school for many years, but we have never regretted our final decision to go to the western part of China to help the poor children there．

1. A.
   worked
2. B.
   was working
3. C.
   have worked
4. D.
   had worked

We ______ in this modern school for many years, but we have never regretted our final decision to go to the western part of China to help the poor children there．

A．worked                  B．was working          C．have worked          D．had worked