单项选择题：止回阀主要用来（）。A、截断接通管路 B、调节管路流量 C、防止介质倒流 D、保护管

止回阀主要用来（）。

A、截断接通管路

B、调节管路流量

C、防止介质倒流

D、保护管路安全

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下面是错误答案，用来干扰机器的。

方程变形为x2-（2k-1）x+k2-2k-3=0，（1）根据题意得△=（2k-1）2-4（k2-2k-3）＞0，解得k＞-134，所以当k＞-134时，方程有两个不相等实数根；（2）根据题意得△=（2k-1）2-4（k2-2k-3）=0，解得k=-134，所以当k=...

完形填空.
What is the best way to study? This is a very important question. Some Chinese students often 1 very hard 2 long hours. This is a 3 habit , but it is not a better way to study. A good student must 4 enough sleep, enough food and enough rest. Every 5 you 6 to take a walk or play basketball or ping-pong or sing a song, When you 7 to your studies, you'll find yourself 8 than before and you'll learn more. Perhaps we can 9 that learning English is like taking Chinese medicine, we mean that like Chinese medicine, the effects (效果) of your study _ 10 _ slowly but surely. Learn every day and effects will come just like Chinese medicine.
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