the children dancing under the tree over there are very happy.为什么用dancing?急用,
问题描述：
the children dancing under the tree over there are very happy.为什么用dancing?急用,
答
这句话的主干是the children are very happy，dancing是用来修饰children的动作的，因为是主动，所以用现在分词形式，意思是在树下跳舞的孩子们十分开心
答
这里是现在分词作定语
其实是由定语从句简化而来的，完整的应该是：
the children who are dancing under the tree over there are very happy.
这里把who 和 are一起省略掉，就可以了
意思是：那些正在那边树下跳舞的孩子们非常幸福快乐。
希望能帮到你！
答
现在分词作定语