关于名词复数的问题
怎么判断名词的复数S应该加在什么地方
例如1“Jim was late for two classes this morning.”he said that he forgot both of the ----.
A.room number B.room number C.room's number D.room numbers
2 After ten years,all those youngsters became____.
A.grown-ups B.growns-ups C.grown-up D.growns-up
在以上两道题中,例1选D,例2选A.应该怎么判断S加在哪个词后面?