in group和in groups的区别

　　They waited at the door in groups to be taken in some conveyance that I couldn't see.

　　他们成群结队地等在门口，让一种我看不见的运输工具载走。

　　When they are young, they live in groups.

　　年幼时，它们过着群居生活。

　　You wouldn't remember me. I was in another group

　　你不会记得我。我那时在另外一组。