Used to do, be used to do sth（被动语态)以及be used to doing sth(to是介词)是我们经常会混淆的use的语法。其中be used to do sth是use的被动用法，指“**被用来做某事”。而be used to doing sth和be accustomed to doing sth一样，表示“习惯于做某事”（注：没有used to doing 这个说法）。这三个用法中比较难且考试经常见到的是used to do的用法：
used to + VERB（原形动词）–过去经常做某事可过去习惯于做某事（目前已不做了），意义和“would often”相同。
- I used to go to the beach every day.
1，Habit in the Past—-表示过去的习惯
“Used to” expresses the idea that something was an old habit that stopped in the past. It indicates that something was often repeated in the past, but it is not usually done now.—“Used to” 表示过去的做法或习惯，但这种做法或习惯已在过去的某个时候停止了。
- Jerry used to study English.
- Sam and Mary used to go to Mexico in the summer.
- I used to start work at 9 o’clock.
- used to eat meat, but now she is a vegetarian.
2，Past Facts and Generalizations—-表示过去的事实
“Used to” can also be used to talk about past facts or generalizations which are no longer true.—-表示过去真实存在的事实，但目前这些事实已不复存在。
- I used to live in Paris.
- Sarah used to be fat, but now she is thin.
- George used to be the best student in class, but now Lena is the best.
- Oranges used to cost very little in Florida, but now they are quite expensive.
3，”Used to” vs. Simple Past—-“Used to”和一般过去式的区别
Both Simple Past and “Used to” can be used to describe past habits, past facts and past generalizations; however, “used to” is preferred when emphasizing these forms of past repetition in positive sentences. On the other hand, when asking questions or making negative sentences, Simple Past is preferred.—-两者都可以表示过去的习惯和事实。但否定句或疑问句一般不用”Used to”，而采用一般过去式。
- You used to play the piano.
- Did you play the piano when you were young?
- You did not play the piano when you were young.