is后面的动词一定要用ing，但是也要具体情况具体分析的，当为be+to do 为将要做某事，或是祈使句。例如：What youve got to do is turn around and say :" Watch me"。为一句祈使句。

is：第三人称he(男) +is ; she(女)+is; it(不是人)+is;其他单数名词+is

例：HeShe is a good student. It is a white cat. A dog is on that street.

is也可与主语缩写,如:

He is = He's, My mother is = My mother's等。但是This is不可缩写。而is与not可缩写成 isn't。

如:This isn't a book. 这不是一本书。