题目

一块边长为的正方形铁片的各角切去大小相同的小正方形,再把它的边沿虚线折转成一个无盖的盒子,若使盒子的容积最大,则切去的正方形的边长为            .   答案：根据所学常识判断下列说法是(√)否(×)正确。(     ) 1. There are always three lights: red, yellow and green. (     ) 2. It's not fast to go by plane. (     ) 3. If you go on foot, you don't need (需要) to know the traffic rules.(     ) 4. In the U. S., drivers drive on the right side of the road.(     ) 5. If the light is yellow, you can go.