题目

在竖直向下的匀强磁场中,将一水平放置的金属棒ab以一水平速度抛出,而且速度方向垂直于金属棒.设棒在下落过程中取向始终不变,不计空气阻力,则金属棒在运动过程中产生的感应电动势的变化情况是（如图所示）（    ） A.越来越大                              B.越来越小C.保持不变                              D.无法判断I had a interesting dream last night. I dreamedthat I took part in a race. At first, I could not to run very fast and fell behind. So I didn’t lose heart and keptrunning. All the students on the playground cheer me on, “ Come on!” I was so encouraging that I ran faster and fast till I caught up all the other runners. I felt as if flying like a superman. In the end, I got to the finishing line first.I won the race. I felt very proudly of myself. Many of my classmate threw me up into the air. Just at that timeI woke up and found me still in bed!