一平行板电容器的两个极板水平放置, 两极板间有一带电量不变的小油滴, 油滴在极板间运动时所受空气阻力的大小与其速率成正比. 若两极板间电压为零, 经一段时间后, 油滴以速率v匀速下降; 若两极板间的电压为U, 经一段时间后, 油滴以速率v匀速上升. 若两极板间电压为-U, 油滴做匀速运动时速度的大小方向将是 A. 2v、向下 B. 2v、向上 C. 3v、向下 D. 3v、向上
（2010·江苏如东高级中学高三国庆假期自主练习一） 14. Although my grandfather is in his eighties, he is still as ______ as a young man and hates sitting around doing nothing al
It was time for breakfast. Mr. and Mrs. Beer were 66. _______ sitting at the table and waiting their daughter Jennet 67. _______ to return back from work. It was late. The parents were 68. ______
