在职攻硕英语考试

【单选题】When I try to understand ______ that prevents so many Americans from being as happy as one might expect, it seems to me that there are two causes.
A．why it does
B．what it does
C．what it is
D．why it is

网考网参考答案：C
网考网解析：
此处是强调句结构it is(what)that prevents so many Americans from being as happy as one might expect... 查看试题解析出处>>