I just don’t understand ________ that prevents so many children at school from b

题干

I just don’t understand ________ that prevents so many children at school from being as happy as one might expect.

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

上一题下一题 0.64难度单项选择更新时间:2011-03-17 09:33:01

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