题目内容：

It is they have seen lots of American films that the learners of English have .
It is _____ they have seen lots of American films that the learners of English have been used to American accents.
A as
B for
C since
D because

优质解答

D
这是强调结构句.如果被强调部分是原因状语从句,只能用because 引导
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