what have they been doing 是什么时态
what have they been doing 是什么时态
what have u been doing的been是什么时态?
have been doing是什么时态?
have been doing sth是什么时态?
have /has been doing 是什么时态
had been doing是什么时态
had been doing 是什么时态?
have been是什么时态?
have+been是什么时态
what have you been doing
what you have been doing
How long have you been doing是什么时态的句子?这个时态怎样构成?