21.    By the end of last week, they           the bridge.

A. has completed          B. completed      C. will complete      D. had completed

22.  The manager as well as the staff _____ chatting cheerfully during the tea break when the boss came in.

    A. were         B. have been            C. was              D. has been

23.  On the east of the city        a collection of high buildings, which has been built up since I lived here.

A. stand         B. stands             C. are stood           D. is standing