21. The use of Chinese by teachers in ______ English classroom must be restricted because it will decrease _______ time when students are exposed to the English language.

A. the; /              B. an; /                           C. /; the                   D. an; the

22. —— I haven’t seen Johnson these days.

—— I think she _______ a conference in Beijing, but I’m not sure.

A. should be attending                      B. might be attending

C. could have attended                       D. must have attended