1、At bay：（经常和keep或hold连用）使……不能接近。One of the gangsters kept the police at bay until the rest escaped。

2、At bottom：实际上。Judy said she was not jealous of her friends success, but at bottom, she was。

3、At close quarters：逼近地。he two rivals grappled at close quarters。

4、At cross purposes：互相误解。I think we are at cross purposes. When I said J.C., I meant Jason Chen, not John Chen。