Look!There are a lot of children playing in the ground.为什么要用playing而不用are playing

题目

Look!There are a lot of children playing in the ground.为什么要用playing而不用are playing

答案

因为前面有 There are 所以再用一个are没有必要
There be .. doing .. 固定的用法
其实也可以把doing 看成定语. 修饰children