12　at work和at rest

　at 可以表示“在做，在……过程中”，后跟不可数名词或单数可数名词，构成固定词组，常作表语，前面用be动词。

Li Ming is at work. 李明在工作／在办公。

They are at rest. 他们在休息。

The children are at school. 孩子们在上学。

They are at their meal. 他们在吃饭。（也可以说at meal ）

Who is at the violin? 谁在拉小提琴？（乐器名词前要用the ）

The two countries are at war. 这两个国家正在交战。