C级轴承的为超精密级，一般用在（）。
参考答案：精密机床或机械上
A．物体加速度大，说明物体速度变化大
B．力是维持物体运动状态的原因
C．重力场中，物体A处在某点的重力势能与物体A无关
D．静电场中，电荷q处在某点的电势能等于把电荷q从该点移到零势点电场力所做的功
Most Americans would prefer to keep their problems _____ themselves and solve their problems _____
themselves. [ ]
A. to, by
B. by, to
C. for, to
D. in, on
