题目

______ they may not succeed, they will try their best. A. Though      B. When      C. Because       D. Unless 答案：A用25牛的水平拉力拉着重为100牛的小车沿水平面匀速运动，小车所受阻力是2525牛；若小车运动的速度是5米/秒，则拉力的功率是125W125W．