I passed all the other course that I took at my university, but I could never pass botany. This was why all botany students had to spend several hours a week in a lab look through a microscope at plant cells, and I could never see through a microscope. This was used to make my professor angry. “I can’t see everything, ” I said. Then he began patient enough to explain how to see through it, but I still couldn’t make it. At last we tried it with every adjustment of the microscope known to men. With my pleasure, I saw something and drew it quickly on the paper. “What’s that?” my professor asked. “That’s what I saw.” I answered. “No, you don’t!” he shouted, and he bent over and looking into the microscope. “That’s your eyes! You’ve fixed the lens so that it reflects! You’ve drawn your eyes!”

地弹簧用于高级建筑物的重型门扇下面的一种自动闭门器。当门扇向内或向外的开启角度不到45度时，它能使门扇自动关闭。