题目

画出相应的入射光线或折射光线。 答案：【答案】略【解析】平行于主光轴的光线折射光线通过焦点画；过光心的入射光线，折射光线的传播方向不变，如图所示：29、 It is about time the government ______ proper steps to solve the traffic problems. A. takes                 B. to take                      C. took                         D. taking