题目

—Is Tom at home?          —No, he ________ to the town. A. has been                B. has gone                 C. goes 答案：B（2008?顺义区一模）骑自行车下坡时，人不蹬脚踏板，车速也会越来越大．请你从能量转换角度对这事实加以解释．