1.be down in a minute 马上就下来

例句：Christopher: I'll be down in a minute.

克里斯托弗：我马上就下去。

2.happened to do 碰巧……

例句：She happened to be out when we called.

我们打电话时她刚巧不在家。

You don't happen to know his name, do you?

你不会碰巧知道他的名字吧？

It happened that she was out when we called.

我们打电话时她刚巧不在家。

3.cover for sb to do sb's work or duties 代替，顶替，替补(某人工作或履行职责)

例句：I'm covering for Jane while she's on leave.

简休假时我来顶替她工作。

4.in the front 在前面

in the back 在后座

例句：He sat in the front of the classroom.

他坐在教室的前面。