I just don’t understand _______ that prevents so many Americans from being as ha

题干

I just don’t understand _______ that prevents so many Americans from being as happy as one might expect.

A．why it does	B．what it does
C．what it is	D．why it is

上一题下一题 0.4难度单项选择更新时间:2015-06-23 07:33:01

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