题目

How to Look After a Computer Many young people use computers, but few of them know how to look after them. Remember the following when you use your computer. 1．    Keep your computer in a cool, dry room.    71   Most computers work best at a temperature of 5℃-30℃. 2．        72    Smoke of all kinds is very bad for many parts of a computer and can cause many problems. 3．        73     Pieces of food and a little water in the keyboard can also cause many problems. 4．    Make sure that the keyboard and screen are at the correct height for you. 质量为m的物体静止在倾角为θ的斜面上，如图所示．已知物体和斜面间的动摩擦因数为μ，则物体受到的摩擦力为_______．若物体在斜面上匀速下滑，则μ与θ间的关系式为_______．