单项填空
21.The teacher dismissed his students with ____ wave of ____ hand a second before the bell rang.
A.a; 不填 B.the; a C.a; the D.a; a
22.Schools that serve healthier foods, offer nutrition education and reward students for nutritious eating habits can make a major ____ in preventing childhood obesity [肥胖].
A.mistake B.sense C.impression D.difference
23.____ else does this kind of forest exist in the world.
A.Anywhere B.Somewhere C.Everywhere D.Nowhere