They have been back这个句子是系表结构吗?been是be的过去分词对吗?为什么后面跟了个原形的back?

Where have they been? The two brothers have never been back < >they left their hometown.A.sinceB.forC.whenD.before 现在完成时have/has gone to,have/has been to,have been in有什么区别The pupils zhe Palace Museum today.They are back now 答案是什么用have/has gone to,have/has been to,have been in填空 Not only his parents but also his brother___to the Summer Palace.They haven't been back.A.have been B.have gone C.has gone D.has been They have been back这个句子是系表结构吗?been是be的过去分词对吗?为什么后面跟了个原形的back? They have a____ been there Have you been back to the piace 为什么说：Where have they been?我知道这是过去完成时,但是为什么不是Where have been they? have they come back yet意思 Not only his parents but also his brother_____ to the Summer Palace.They haven't been back.A.have beenB.have goneC.has beenD.has gone someone whose smile makes me feel i have been holding back now.这句话怎么翻译? what have they been doing 是什么时态 What places have they been?怎么翻译? where have they been?是现在完成时吗? they have been in kate's for they have been the subject of debate they have been acting up more lately they have been there before.so have i they have been there before.(),() 改为同义句