Exercise is good (19)_______us because it keep us fit. It not only makes ours muscle strong (20)_______helps us think better. After an exercise, we sleep more soundly and wake up (21)______ fresher. It is good to exercise outdoors where there is plenty of fresh air and sunlight. Sunlight kills germs and help our bodies to make vitamin D (22) _______ makes our bones strong. Fresh air contains more oxygen. We breathe it more deeply and (23)_________while exercising, so we get more oxygen into our bodies and clear out the harmful air. This is why you usually feel better (24)_______we have exercised 19. A. at B. to C. for D. with 20. A. but also B. but for C. as well D. also 21. A. feel B. to feel C. felt D. feeling 22. A. what B. that C. it D. how 23. A. fast B. quick C. faster D. quicker 24. A. after B. before C. during D. until