选哪个并解释原因He hasn't come to class yet.What do you think------?

He hasn't come to class yet.
What do you think______?
答案是 B.has happened to him
do you think 可以看做插入语
这是对主语提问
选项A 是被动语态 happen是不及物动词 没有被动语态形式 应首先排除
选项 C.do you think 已经是疑问语序 后面应该是陈述句语序
另外happen 当发生讲 主语不能是人
选项 D.has he happened 应把he 去掉
注意 本句的主语 是what