I live in a nice new building in Beijing. It is very tall. It has eighteen floors. There are about eighty families in the building. That is to say (也就是说), about two hundred and forty people live in the building.

    My home is on the twelfth floor. We have two bedrooms and a living room. They are big and clean. There are a lot of big trees and beautiful flowers around our building. I like looking out of the window in my room. I can see cars and buses running in the street. I can see people walking in the street, too. They look so small! I can also see a lot of tall buildings. How beautiful Beijing is! I am happy to live in this nice, new and tall building.

下列四幅图中，磁感线的方向、磁极名称标注正确的是(     )

读 《最苦与最乐》，在作者笔下，贫而不苦的原因是____，失意而不苦的原因是____，老、病、死而不苦的原因是____。

如图所示，透明塑料盒的底部开有小孔，电子式火花发生器的放电针管紧紧地从孔中塞进。打开塑料盒盖，向盒中滴入数滴酒精，再将盒盖盖紧，摁动电火花发生器的按钮，塑料盒盖立即被远远地弹出。