为什么在“Look at this group of people playing beach velleyball"中,没有助动词be.

题目

为什么在“Look at this group of people playing beach velleyball"中,没有助动词be.
Thank you jioning CCYV's Around The World show.Today,we're in Australia.It's a beautiful,sunny day!There are many people here on vacation.Some are taking photos.Others are lying on the beach.Look at this group of people playing beach volleyball.They look cool!
动词的现在分词的构成是助动词be+动词ing.在“Some are taking photos”和“Others are lying on the beach”中,都有助动词be.为什么在“Look at this group of people playing beach velleyball"中,没有助动词be.

答案

这个句子实际上是一个省略句,完整的句子是：look at this group of people who are playing beach velleyball.其中who are 开始,整个后面的内容做定语,因此是一个定语从句,这样的句子who are是可以省略的.