They have been doing their homework能改成：he has been doing their homework 吗?have改成了has

what have they been doing 是什么时态 have been doing sth They have been doing their homework能改成：he has been doing their homework 吗?have改成了has they shoud never do what they have been doing for many have been doing 神马意思? what you have been doing Where have they been? has been doing have been done区别 They can’t have been doing their homework ---doing是什么词性?have been 在这里还是表现在完成时吗 have been doing ,have done和have doing区别 i has been doing 还是i have been doing They can't have been doing thier homework.have been 是现在完成时,但是后面do为什么要变成doing?They can't have been doing thier homework.这句话 have been 是现在完成时,但是后面do为什么要变成doing?为什么不用do呢? 现在完成进行时的被动语态结构是have been +过去分词还是have been+doing例如：They have been collecting some stamps since2000Some stamps have been collected by them since 2000 have been doing 为什么还有 have been deadj have been do和have been doing的不同 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 a____ been there have been doing,had been doing,will have been down是什么