问题
选择题
His mother had thought it would be good for his character to ________ from home and earn some money on his own.
A．ran away
B．take away
C．keep away
D．get away
答案
D
get away from home离开家；ran away 逃走；keep away避开。
．G为万有引力常数，M、m表示星球与物体的质量，而万有引力做的功则为引力势能减少．已知月球质量为M、半径为R，探月飞船的总质量为m，月球表面的重力加速度为g，万有引力常数G．
，将（1）中的
代入即可．请判断此方法是否正确，并说明理由，如不正确，请给出正确的解法与结果．（不计飞船质量的变化及其他天体的引力和月球的自转）