以下关于Internet的知识不正确的是（）
A、起源于美国军方的网络
B、可以进行网上购物
C、可以共享资源
D、消除了安全隐患
参考答案：D
50千克小麦磨出40千克的面粉，小麦的出粉率是8%。[ ]
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
