Most cities and towns in China have night markets(市场). During the day, these streets are quiet. At night, they become crowded(拥挤的)and lively. Usually, people get there at three or four in the afternoon. By 6:00, the streets are like rivers of people. Night markets are fun places to shop. You can buy clothes, shoes, and many other things. If you think the price is too high, you can bargain with the seller. You can also buy nice food. When you are hungry, you can sit down for a meal. Smelly tofu is popular, but it really smells bad! The best thing is that everything in night markets is cheap!

家兔属于哺乳动物，胎生、哺乳相对于其他生殖方式的优势在于：

    We spend hours, days and years of our lives in school. Imagine(想象) you could design(设计) your dream school, what would it be like? What would you be doing? We wanted to find out what teenagers around the world thought. Here is what they said:

    Richard from the USA: My dream school would have a big swimming pool and two soccer fields. It would also have a cinema, a gym and a shopping centre. My school has none of these, and I think there should be more pleasant things for students to do while they are studying.

    Sonia from Italy: I'd like a room where we can relax and play computer games. I'd also like to have a music room. I think there should be a place for everyone to go and relax after class.

    Wu from Beijing: I think it would be great to have another day off (休息日) every week, besides the weekend. If that day was a Friday or a Monday, we would have a long weekend every week. What fun! I also think school should start later, at about 10 o'clock, and finish earlier.

    Hannah from Australia: In my dream school, I think the teachers should give us more freedom(自由) and choice about how we study and what we study. I also think it's not necessary for us to wear school uniforms every day. I really don't like wearing it.

一人乘电梯上楼，在竖直上升过程中加速度a随时间t变化的图线如图所示，以竖直向上为a的正方向，则人对地板的压力（  ）