when是什么意思啊？

when在英语里有三种词性：

特殊疑问词，“什么时候”，后面跟一般疑问句语序。如：

When were you born?

When will the class begin?

When do you start work and finish work?

从属连接词，“当什么时候”，引导时间状语从句，后接陈述句的语序，如：

He always helps me when I am in trouble.

When my dad came back, I was watching TV.

缩合连接副词，引导名词性从句。

This was when I was born.

Do you know when the class will begin?

I don't know when they will achieve the goal.

此外，疑问副词when后面加动词不定式to do（注意，when后面没有接动名词doing的用法），可以作句子的主语，表语、宾语等，如：

I don't know when to use the sentence pattern.

When to go is a problem.

The problem is when to begin the class.