be at war（正在交战）：The two countries are at war now．两国正在交战。

　　（相当于：The two countries are waging a war now．）

　　be at work（正在工作）：Jim is at work on his car now．吉姆正在修自己的车。

　　（相当于：Jim is repairing his car now．）

　　be at peace（处于和平或平静状态）：

　　Thus Europe was at peace for the first time in ten years．

　　于是欧洲在十年以后第一次进入和平状态。

　　be at table（正在吃饭）：When I arrived my friends were already at table．

　　当我到达时，我的朋友们正在吃饭。

　　常见的这类结构还有：be at meeting正在开会；be at school正在上学；be at breakfast（lunch ／supper）正在吃早（午／晚）饭；be at church正在做礼拜，等等。