题目

如图所示，固定的竖直光滑U型金属导轨，间距为L，上端接有阻值为R的电阻，处在方向水平且垂直于导轨平面、磁感应强度为B的匀强磁场中，质量为m、电阻为r的导体棒与劲度系数为k的固定轻弹簧相连放在导轨上，导轨的电阻忽略不计．初始时刻，弹簧处于伸长状态，其伸长量为x1=，此时导体棒具有竖直向上的初速度v0．在沿导轨往复运动的过程中，导体棒始终与导轨垂直并保持良好接触．则下列说法正确的是（）     A． 初始时刻导体棒受到的安选择正确的词组,并用其适当形式填空(10分，每空1分) take place;        in the shape (of);        before long;     set off;  look forward to;       lose weight;         be curious about;    be tired of;        earn one’s living         keep one’s word;1. I have eaten the same food for a month, now I ____________it and I will never try it any more.2. After graduation, she’s going to __________ by working on her father’s farm.3. We can believe him, he always__________.4. At the Festival of Halloween, children usually dress up _________ ghosts.5. The holiday that everyone______________ has come. 6. Mr. Greens will _________ for Beijing tomorrow. 7. The child in African had no enough food, _____________, she staved to death. 8. If you _____________Australian cities, just read the book written by Dr. Johnson.9. The best way to________ is keeping on doing exercise. 10. We have never discovered what __________ between the couple that day.