3.省略一个从句或从句的一部分，可用so 或 not代替。常用于此类的动词有believe , think, expect, guess, hope, imagine, suppose, say, tell等以及appear, seem, afraid etc
1) –Is he coming back tonight? --I think so
2) –She must be busy now? --If so, she can’t go with us.
3) –Is she feeling better today? --I’m afraid not
4) –Do you think he will attend the meeting?
