时态语态　 主动　被动
一般式　 to doto be done
进行式　 to be doing
完成式　 to have done to have been done
完成进行式　 to have been doing

1) 现在时：一般现在时表示的动词，有时与谓语动词表示的动作同时发生，有时发生在谓语动词的动作之后。
He seems to know this.
I hope to see you again. = I hope that I'll see you again.　我希望再见到你。

2) 完成时：表示的动作发生在谓语动词表示的动作之前。
　I'm sorry to have given you so much trouble.
　He seems to have caught a cold.

3) 进行时： 表示动作正在进行，与谓语动词表示的动作同时发生。
　He seems to be eating something.

4) 完成进行时：
　She is known to have been wreaking on the problem for many years.