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问题 单项选择题

现将关系模式P分解为三个关系模式P1(A，B，D，E，F)，P2(A，B，G，H)， P3(C，I，J)，则其中P2的规范化程度达到( )。

A．1NF

B．2NF

C．3NF

D．BCNF

答案

参考答案：B

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Healthy teeth are important in many ways. For example, when we get our pictures taken, everyone says “Say cheese!” So we open our mouth and show our teeth.

小题1:Strong and healthy teeth help us chew the right food to grow. They also help us speak clearly and look our best. 小题2:我们必须照顾好我们的牙齿。What should we do to protect our teeth?

First, we should brush them at least twice a day—after breakfast and before bedtime. We should brush all of our teeth, not just the front ones. 小题3: We should spend at least 3 minutes each time brushing teeth.

小题4:一年看两次牙医也很重要。Besides checking for disease, the dentist will help keep our teeth extra clean.

小题5:We also need to be careful about what we eat and drink. Remember to eat more vegetables and fruit and drink more water. Of course, don’t forget to smile!
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单项选择题

频谱多普勒滤波调节原则为

A．低速血流用高通滤波

B．高速血流用低通滤波

C．低速及高速血流均用低通滤波

D．低速及高速血流均用高通滤波

E．低速血流用低通滤波，高速血流用高通滤波
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