谈Call in, Call on, Call at, Call for

Call in 作请来、找来、召来解，请人来作某种专业的咨询或帮忙的意思。如：

Your father is ill， you should call in a doctor at once.你父亲病了，应该马上去请个大夫来。

The police have been called in to help make it clear.

已请来了警察帮忙把这件事弄清楚。

Call on和call at的意思一样，都是拜访访问，但call on后接表示人的名词或代词，call at 后接表示地点或场所的词语。试比较：

I called on the Smiths yesterday.

我昨天拜访了史密斯一家人。

I called at the Smiths yesterday.

我昨天去了史密斯家。

I called on the doctor yesterday.

我昨天去拜访了医生。

I called at the doctors yesterday.

我昨天去了医务室。

另外，call on还可以号召，后面往往接动词不定式作宾语补主语。如：

The headmaster called on the students to work harder.校长号召学生们更努力地学习。

Call for 有几个不同的意思：

1.作要求、需要、提倡解。如：

Success calls for hard work.

成功要靠勤奋。

People are calling for the freedom of all slaves.人们要求解放所有奴隶。