不定式的特殊句型so as to

　　1) 表示目的;它的否定式是so as not to do。

　　Tom kept quiet about the accident so as not to lose his job.　汤姆对事故保持沉默是为了不丢掉他的工作。

　　Go in quietly so as not to wake the baby. 轻点进去，别惊醒了婴儿。

　　2) so kind as to ---劳驾

　　Would you be so kind as to tell me the time? 劳驾，现在几点了。

　　不定式的特殊句型Why not

　　"Why not +动词原形"表达向某人提出建议，翻译为："为什么不……?" "干吗不……?"

　　例如：Why not take a holiday?　干吗不去度假?

　　不定式的时态和语态

　　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.