join是终止型动词 be in和be on是延续型 系表词组 join的延续性动词 可以用 be in和be on in和on 的用法 要看 后面的 介词宾语， 加入某种组织要用in. 如army， party, club等 he has been on his school team for two years. he has been in the army for two years.
