题目

下图是小明自制的游戏打桩机的示意图.它利用光学元件改变太阳光的传播方向，从而烧 断细线，使重锤下落打在桩上.图中元件a为       镜，元件b为       镜.重锤在下落的过程中，       能转化为动能. 答案：平面  凸透   重力势My parents ______ born in Shanghai, but I ______ born in Nanjing.A. was, was B. were, was C. were, were D. are, am