根据图中给的入射光线和折射光线，在方框内画出一个适当类型的透镜。
Look and answer. Bill一周内吃了多少食物？
1. How often does Bill eat cabbage?
2. What vegetable does Bill eat three times a week ?
3. What is Bill's favourite food?
4. What food does Bill eat less?
在什么情况下容易产生操作过电压？
