used to do sth. 　过去常常做某事
　　普通句： I used to take diet pills.
　　我过去吃过减肥药丸。
　　次级高手句： I used to take diet pills and eat diet food.
　　我过去吃过减肥药丸和减肥食品。
　　高手句： I used to take diet pills and eat diet food for one year.
　　我过去吃减肥药丸和减肥食品有整整一年。
　　超级高手句： I used to take diet pills and eat diet food for one year when I was in college.
　　我过去在学校的时候吃减肥药丸和减肥食品有整整一年。
　　专家句： I used to take diet pills and eat diet food for one year when I was still in college.
　　我过去还在学校的时候吃减肥药丸和减肥食品有整整一年。