为了避免重复，或为了使句子更简练，在一些句子中常常省去一个或几个成分，这种语法现象叫省略。
[观察例句]
①(You)Come in，please!
②(Are you) OK?
③(You come) This way，please.
④John is a lawyer，and his wife (is) a cleaner.
⑤The boy wanted to play football in the street，but his mother did not allow him to(play football in the street)．
⑥His advice made me happy，but (his advice made) Jim angry.
⑦You'd better look out when (you are) crossing the street.
⑧He is the man (who/whom/that) you can depend on.
⑨He said (that) the text was very important and that we should learn it by heart.
