如图所示，两木块A、B叠放在水平桌面上，现以水平拉力F拉B没有拉动，则以下说法正确的是（ ）
A．A、B间不存在摩擦力作用
B．A、B间有静摩擦力作用
C．B与桌面间有静摩擦力作用
D．若撤去外力F后，则A与B、B与桌面间都没有摩擦力
A、B以A为研究对象，A相对于B没有运动趋势，不受B的摩擦力，即A、B间不存在摩擦力作用．故A正确，B错误．
C、以A和B整体为研究对象，水平方向受到拉力F，根据平衡条件得知，桌面对B有向左的静摩擦力，大小f=F．故C正确．
D、若撤去外力F后，A与B、B与桌面间都没有相对运动趋势，则A与B、B与桌面间都没有摩擦力．故D正确．
故选ACD
阅读短文，根据短文内容，从短文后得选项中选出能填入空白处的最佳选项。选项中有一项为多余选项。（共8分，每小题2分） Bill Gates is a very important person in the computer industry. He has been chief officer of Microsoft Company for several years. He is also the richest person in the United States. How did he do it? He learned a lot from his parents. While Bill was going to school, his father went to college, got a degree, and became a successful lawyer. 1 . His mother was a very busy teacher, but she also loved going to parties. From this, he learned something else: if you want to work hard and play hard, you have to make a schedule. 2 . While most of his friends were playing, Bill read all of the World Book Encyclopedia and finished it when he was 8 years old. 3 . He used to play a lot of sports — swimming， water-skiing, tennis. When Bill got older, he spent more and more time working and playing on a computer. Before he was twenty, Bill developed the world’s first computer language for the personal computer. 4 . He thought that every home was going to have a computer, and every computer would need software — his software. He said, “ I’m going to make my first million dollars on software by the time I’m 25.” And he did!
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