1 动词加ing形式,作为动词不能单独出现要加be动词,或者是 have / has been doing :
------ She is coming by taxi
-------- She has been coming to see us for years.
2 作为形容词可以单独出现
------- His story is qiute moving / touching / tear-inviting.
3 动词加ed形式,作为动词表示被动不可以单独出现,必须是 be + 过去分词：
He was invited here (被动语态).We invited him here (主动语态).
4 也可以做为形容词单独出现：
The ball game was exciting ,and he was excited about it .