一道英语选择题：They ___ since they left last July.（ ）They ___ since they left last July.A.had been away B.have been away对的话,请说一下理由.

since
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DJ: []
ad.(常用于现在完成时或过去完成时)
1. 此后;从那时到现在
She left school three years ago and has worked as a nurse ever since.
她三年前毕业,从那时起便一直当护士。
2. 之前,以前
prep.
1. (常用于现在完成时或过去完成时)自...以来,从...至今
I haven't heard from him since last year.
我自去年以来未曾收到过他的信。
conj.
1. (常用于现在完成时或过去完成时)自...以来,从...至今
It's been ten years since they married.
他们结婚到现在已经十年了。
She has been living a hard life since her husband died.
她自从丈夫死后,一直过着艰苦的生活。
2. 既然;因为,由于
He must have taken the book since it isn't here.
他一定是把书拿走了,因为书已不在这里了。
Since it is so hot, let's go swimming.
既然天气这么热,我们去游泳吧。
现在完成时的公式是:
have/has + 动词过去分词
所以答案选B.

给我五分，我给你说

答案是B,用A的话有歧义,此句的意思应该是他们离开后一直还没回来,所以选B.