请问they have been able to do的时态是什么?been able to 和 be able to的区别是什么?

Where have they been? They have a____ been there 英语?They will have been married for 20 years by then.请问been在句中作什么成份, 请问they have been able to do的时态是什么?been able to 和 be able to的区别是什么? 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 They can't have been doing their homework请问can't have been是对刚才所发生的事的推测吗? They have been here once.把been换成came怎么样 they said they have been married for ten years They have never been opened.为什么不可以是They never have been opened. they have been here since 1988,对1988进行提问,（）（）have they been here? They have been friends for 6 years. 改为同义句 They have been friends _______ _______. They have been skating for five hours 同义句 They have been skating_______ _____ ________ ______