Question

名词性从句When I try to understand ____ that prevents so many Ame

Answer 1

我对语法的技术性用语了解不透彻,但是可以帮你剖一下这个句子,应该可以帮到楼主.
首先看整个句子,when I do sth,it seems to me ...所以这个东西在时间状语里面,和后面的主句没有关系.（主句故意用了reason果断就是干扰,换成别的i want to eat什么的都不影响）
在when的从句里面,i try to understand sth,考点就是把这里的sth给放大了
sth = what it is that does sth用了倒桩是因为跟在陈述句里面作宾语
调整语序为what is it that does sth
所以整个宾语是个原句为强调句式的疑问倒装句
给一个逻辑链：when I try to understand A,it seems to me that ...
it is A that prevents so many Americans ...
这个A就是what,就是说话人不明白的地方.
如果换成why：when I try to understand why so many Americans are NOT as happy as one might expect,it seems to me ...（我不知道为什么这么多老美不像想象的那么开森.）
原句意为：我不知道到底是什么让老美没有想象的那么开森.
不知道有帮助没.