CALL IN CALL ON

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 Smith's 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 doctor's 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 in 用于召集专业人员，如call in a doctor
call on 用于拜访某人

call at someplace
call on sb.
call in
1. 请求收回;请来