exercise
1.exercise统指“运动”。例如：We take exercise every morning. We take several forms of exercise every morning. 和Walking is good exercise. an（或a...）exercise是“一种运动”。例如：Walking is a good exercise. exercises是“各种运动”。例如：Walking and riding are good exercises.
2.exercise在用作“习题”解的时候，后面接in和科目名称，或on或in和科目的部分的名称，如an exercise in English grammar和an exercise on（或in）the construction of conditional sentences。
3.graduation（或graduating）exercises（毕业典礼），inauguration exercises（就职典礼或开幕典礼）等是美国英语，exercises相当于英国的ceremony或ceremonies。
4.take exercise和exercise用作不及物动词都作“体操”或“运动”解，不指一般的“作练习”。
5.不可说We exercise in boxing once a week，该说We are exercised in boxing once a week。
