后边加复数，例如：
1、A group of kids were playing with a ball in the street.一群孩子在街上玩球。
2、There was a group of youths standing on the street corner.有一群年轻人站在街角。
3、The story is built around a group of high school dropouts.故事围绕着一群辍学的中学生展开。
a group of +名词，表示一个什么团队（小组），是单数。例如
this is a group of cave exploration
这是一个山洞探险队
