We have twenty minutes' rest between classes. Look! Most of us are playing during the break time. Some students are on the playground. They are playing basketball. Oh! A boy is running with the ball. And another is trying to stop(阻止) him. They look so cool. And there are some girls watching the game. Some students are in the classroom. They are talking. A few of them are reading and doing homework. Look!  A girl is looking at the birds in the tree in front of the classroom. She must be thinking of something interesting because she is smiling. What are the teachers doing? Some of them are working in the office. And some are talking with students. Everyone is doing his or her things. They are busy but happy.

科学兴趣小组为探究CO₂的多少是否会影响光合作用的强度，在家里做了如下的实验：

在某植物的叶片上剪下大小相同的多个叶圆片，抽出叶圆片中的气体（图如甲），然后，置于不同浓度的NaHCO₃溶液中（如图乙），测量每个杯子中叶圆片从杯底上浮至液面所需的平均时间．

注：NaHCO₃能增加溶液中CO₂的含量，叶圆片吸收CO₂释放O₂，部分O₂存在于细胞间隙和叶圆片边缘，导致叶圆片上浮．

    Now more and more people in the world are getting fatter. This troubles them a lot. （1）Experts(专家) say that it has a lot to do with our eating habits.
    Our eating habits are very important for good health and a strong body. Most of us like eating sweets and ice cream better than vegetables and rice. Sweets and ice cream are not bad for us if we eat them at the end of a meal. （2）If we eat them before a meal, they may take away our appetite(食欲).
    It's important for us to eat our meal in the same period each day. When we feel worried or excited, we may not want to eat. A long time ago, in England, some judges(法官) often decided whether a man was telling the truth by giving him some dry bread. If the man could not swallow(吞) the bread, it meant that he wasn't telling the truth. Because when a man is worried about something, he will have trouble in swallowing anything dry, because he loses his appetite.