题目

（16分）如图所示，足够长的光滑导轨ab、cd固定在竖直平面内，导轨间距为l，b、c两点间接一阻值为R的电阻。ef是一水平放置的导体杆，其质量为m、有效电阻值为R，杆与ab、cd保持良好接触。整个装置放在磁感应强度大小为B的匀强磁场中，磁场方向与导轨平面垂直。现用一竖直向上的力拉导体杆，使导体杆从静止开始做加速度为的匀加速运动，上升了h高度，这一过程中bc间电阻R产生的焦耳热为Q，g为重力加速度，不计导轨电阻及感应电流间的相互作     Today the children of this country at last returned to work. After two months holiday pupils have started a new term. How many adults (成年人) get such a long holiday? Two or four weeks in the summer and public (公共的) holidays —that’s all workingmen get. For most women,they are not lucky to have a holiday at all.    Children don't need such a long holiday. In term time they start work later and finish earlier than anyone else. In holidays,most of them get bored,and some get into trouble. What a waste!If their parents had more free time instead,everyone would be happier. This is not just a national problem,either—it is worldwide. Dates may be different from country to country,but the pattern (模式) is the same,why should children do half as much work and get twice as much holidays as their parents?() 1. Most workingmen get weeks in the summer and public holidays.   A. three and five   B. two or four   C. four and six   D. two or six() 2. From the passage we know that .   A. it is not easy for a woman to get a holiday   B. most women have holidays   C. no woman gets holidays   D. most men don't have holidays() 3. The writer thinks children .   A. must have such a long holiday   B. should have a long holiday   C. don't need such a long holiday   D. should get into trouble in holidays() 4. How long do children have for their holidays?   A. Two weekvS.     B. Two days.   C. Half of their parents’ holidays.    D. Twice of their parents’ holidays.() 5. Children in have long holidays.   A. few countries   B. many countries   C. just this country   D. a few of countries