There are birds flying in the sky.=There are birds which are flying in the sky.
解答:flying in the sky为现在分词短语作定语,修饰前面的名词“birds”,相当于定语从句“which are flying in the sky”。
There are some boys playing games on the playground.=There are some boys who are playing games on the playground
有些男孩子在操场上做游戏。备注:以上结构属于“There be+名词+现在分词(doing)结构,名词是后面现在分词逻辑主语。”