我国自行设计建造的世界第二斜拉索桥——上海南浦大桥，桥面高46 m，主桥全长845 m，引桥全长7500 m，引桥建得这样长的目的是 ( )
A．增大汽车上桥时的牵引力
B．减小汽车上桥时的牵引力
C．增大汽车的重力平行于引桥桥面向下的分力
D．减小汽车的重力平行于引桥桥面向下的分力
答案：D
引桥越高，斜面倾角θ越小，重力沿斜面方向的分力F＝mgsinθ越小，故D对．
| 完形填空。根据短文，选择最佳选项。 |
| It's four o'clock in the afternoon. It's time 1 . But we 2 our classroom. There 3 seven students in our team(组). Now, there are only five. I say to Bill, come and clean (弄干净) 4 classroom. Look! Jane and Tom 5 the chairs and desks. One of us 6 carrying water. Lily, Lucy and I are cleaning the floor. What is Jim 7 ? We 8 him in the class room. 9 is he? Do you 10 ？ |
| ( ) 1. A. to go home ( ) 2. A. clean ( ) 3. A. is ( ) 4. A. our ( ) 5. A. is putting ( ) 6. A. am ( ) 7. A. saying ( ) 8. A. can see ( ) 9. A. What ( ) 10. A. know | B. go home B. cleans B. have B. you B. are puting B. is B. having B. find B. Who B. go | C. go to home C. must clean C. has C. your C. putting C. are C. doing C. can't find C. When C. like | D. goes to home D. cleaning D. are D. us D. are putting D. be D. do D. aren't see D. Where D. look |