题目

Once upon a time, on Christmas Eve, Scrooge sat in his office. The door of his office was open. He wanted to keep his eyes on his clerk, Bob Cratchit. Bob sat in a cold, gloomy, little cell. Scrooge had a very small fire, but Bob’s was even smaller. Bob couldn’t add any more coal because Scrooge kept the coal scuttle in his room.“A Merry Christmas, uncle!” cried a happy voice. It was Scrooge’s nephew Fred.“Bah!” said Scrooge. “Humbug! Merry Christmas! What reason have you got to be merry? You are poor.” “OK, then,” replied Fred cheerfully. “What reason have you got to b小球做匀速圆周运动，半径为R，向心加速度为a，则(    )A.小球的角速度为          B.小球的运动周期C.小球的时间t内通过的位移   D.小球在时间t内通过的路程