四冲程柴油机工作时活塞改变运动方向的瞬时位置称为（）。
A、零点
B、支点
C、定点
D、止点
参考答案：D
髋的骨性关节炎最常见的表现是
A．关节渗液
B．疼痛
C．捻发音
D．关节挛缩
E．无力
I was about to give up my effort to work on the puzzle when a good idea _____ me. [ ]
A. beat
B. struck
C. attacked
D. caught
about to give up my effort to work on the puzzle when a good idea _____ me. [ ]