一道高中英语选择题(twice a year)

题目

一道高中英语选择题(twice a year)
_____ twice a year , whether it is a car or a bus or a truck ,is the role that everyong must obey in the city.
A.Examined
B.Being examined
答案是B
A为什么不对?
谢谢

答案

分析句子成分：
_____ twice a year －－－－主语
whether it is a car or a bus or a truck－－－插入语不必考虑成分
is －－－谓语动词
the role that everyong must obey in the city.－－－宾语
再考虑能充当主语的名词、代词、动名词、不定式等.
而被动式放在开头只能充当状语,表示与主语之间是被动关系.所以,为了使句子成分完整不缺主语且保持与主语被动关系用being examined.
答案是正确的.