题目内容
What ________ before printing was invented?
[ ]
A.has happened
B.was happened
C.happened
D.has been happened
答案:C
解析:
解析:
|
happen是不及物动词,无被动语态,故排除选项B、D.另外before状语从句是过去式,故不能与A项连用. |
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