21.—Children should be allowed more time to do sports.
— __________. Many of them are suffering from obesity.
A. All right B. Exactly C. Go ahead D. Fine
22. He goes to work by ____subway while she takes ____ bus to work
A. the / B. / the C. / a D. a /
23. Some students find __ difficult ___ English
A. / to study B it to study C / studying D it studying
