肺泡与气体交换相适应的结构特点是（ ）
A．肺泡数目多
B．肺泡外缠绕着许多毛细血管
C．肺泡壁与毛细血管壁都只是由一层上皮细胞构成
D．以上都是
答案：D
题目分析：呼吸系统的组成包括呼吸道和肺两部分．呼吸道包括鼻腔、咽、喉、气管、支气管，是呼吸的通道，呼吸道保证了气体的畅通．肺由许多肺泡构成，气体交换的效率高；肺泡外面包绕着丰富的毛细血管和弹性纤维，肺泡的壁和毛细血管壁都很薄，只有一层上皮细胞构成，这些特点都有利于气体交换，因此肺是气体交换的主要场所．
信息归纳(共5小题，每小题1分，共5分) “USA? Britain? Which country is the better to study in ?” We often hear such discussions. As China opens its door, it’s a dream for many Chinese students to study abroad. They want to learn about the outside world. It’s true that studying abroad can help students develop themselves. Their foreign language skills will be improved and it may be easier to find jobs. But there are problems that should be considered. Language is the first. Students must spend a lot of time to learn another language. Students must also learn to live without parents’ care and deal with all kinds of things they haven’t done before, like looking after themselves. There are reports about Chinese students abroad running into an ocean of difficulties and giving up finally when they have to take care of themselves. It’s hard for students to study well. Finally, studying abroad brings a heavy burden to the family. For most Chinese parents, the cost of studying abroad is very high. But is it worth ? We know that there are many famous people who have achieved success through their hard work in China. Liu Xiang is a good example. Once an American coach invited him there, but he refused. He kept training hard with his Chinese coach. He surprised the world when he won a gold medal at the Athens Olympic Games. So when you wonder which country is better to study in, think it again. Information Card
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