题目

下列说法正确的是（ ） A . 物体经凸透镜只能成实像 B . 在折射现象中，光路是不可逆的 C . 当光从空气射入玻璃中时，传播方向一定会发生改变 D . 跟主轴平行的光线，经凹透镜折射后，不能形成一个最小、最亮的光斑 答案：DI looked at the young man, wondering ________ . [　　] A．when had I seen him before B．that where I had seen him before C．if I saw him before D．whether I had seen him before