It worries the couple a lot _______ their only son is behaving worse and worse these days.
问题描述：
It worries the couple a lot _______ their only son is behaving worse and worse these days.
A.how B.why C.that D.what
选哪个,为何?
答
选择C项.这是个that引导的主语从句.it是形式主语,真正的主语就是这个that从句（从that开始一直到句子末尾这一部分）.意思“他们的独生子这些日子以来表现越来越差”使夫妻俩忧心忡忡.
其他三项都是有疑问意思的连接词,但这个从句其实就是个陈述句,没有疑问的意思,所以不选它们.