请帮我解释一下几个词组．

call at:

vt. 访问(停靠)

例句与用法:
1. The ship called at several ports between Dalian and Shanghai.
这艘船在大连和上海之间停靠了几个港口。

2. I shall call at his home tomorrow.
我明天要到他家里拜访。

3. I wanted to call at him the minute he arrived.
我刚要打电话给他, 他就来了。

4. I'd love to, but my father's go to call at me.
我倒是希望来的，可是我的父亲要来看我。

5. The postman always calls at 7.30.
邮递员一贯7时30分来.

英英解释:
动词call at:

1. enter a harbor
同义词：out in

call on:

vt. 号召(约请,访问)

例句与用法:
1. Our salesmen call on their best account twice a month.
我们的销售人员每月访问最好的客户两次。

2. The government calls on the youth to donate their blood voluntarily.
政府号召青年义务献血。

3. Tomorrow I'll pay a call on him.
明天我将要去拜访他。

4. I'd like to call on you this Sunday.
我想这个星期天来找你。

5. If I were free now, I