Do you find that when you are busy with your study on the Internet, the speed of your computer slows down   小题1:  sometimes? It is probably because your computer gets infected by virus (病毒), which can make it more difficult for you to use the computer. How to keep viruses小题2: your computer is a problem now. But in fact, nothing can ensure (保证) the security of your computer one hundred percent. There are, somehow some things you can do to  小题3: your computer’s security system and decrease (降低) the possibility of an infection.

You can   小题4: your system up to date with the current anti-virus software (反病毒软件), and use the following methods

液压系统的泄漏现象是由泄漏间隙（）造成的。

A.大小

B.液体温度

C.液体稠度

D.两边压差