下图是人体肺部与血液进行气体交换示意图，根据图回答：
（1）肺泡是气体交换的场所，在肺泡外包绕着丰富的 ，它们的壁都是由一层 构成，有利于气体交换。
（2）肺泡中的氧气，依次穿过
和 两层壁扩散到血液里。
（1）毛细血管，上皮细胞（2）肺泡壁 毛细血管壁
题目分析：（1）肺是呼吸系统的主要器官，它是气体交换的主要场所，肺是由支气管在肺内不断分支，在最末端形成肺泡，肺泡是由一层扁平的上皮细胞组成，肺泡外面缠绕着毛细血管，毛细血管也是由一层扁平的上皮细胞组成，这有利于肺泡和血液之间进行气体交换。
（2）肺泡中的氧要进入血液，首先要穿过肺泡壁，再穿过毛细血管壁，进入血液中。
How to be a healthy kid Hi, boys and girls! Do you know how to be a healthy kid? Here are some rules you should follow. First, eat different foods, especially fruit and vegetables. You may have a favorite food, but you should eat something different. If you eat different foods, you will probably get more nutrients (营养) your body needs. Second，drink water and milk as often as possible .When you are really thirsty, cold water is the first choice. Milk is a great drink that cangive you more calcium your body needs to grow strong bones. Third,”listen” to your body .How do you feel when you are full?When you are eating ,notice how your body feels when your stomach feels comfortable ,eating too much will not make you feel comforbable and will make you fat. Fourth, limit (限制) screen time. Screen time is the time you watch TV, DVDs and videos, or using computers. It is good to take more exercise such as playing basketball, swimming and so on. You can't watch TV for more than two hours a day. Fifth, be active. One thing you should do is to know which activity you like best. Find ways to be active every day. Follow these rules and you can be a healthy kid.
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