下列叙述中，与肺的气体交换作用有关系的是（ ）
A．肺泡的数目多
B．肺泡外面包绕着毛细血管
C．肺泡壁和毛细血管壁都是由一层上皮细胞构成
D．以上都是
肺是呼吸系统的主要器官，是气体交换的主要场所，肺泡是气体交换的主要部位．肺泡数目极多，增大了肺进行气体交换的面积，肺泡外包绕着毛细血管，有利于气体在肺泡和毛细血管内的血液之间进行气体交换，肺泡壁只有一层上皮细胞，有利于物质出入．综上所述：A、B、C选项均符合题意；
故选：D
| 阅读理解 | |
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| 1. The reading above is in fact ________. | |
| A. an advertisement B. a report C. a notice D. an invitation | |
| 2. When you are accepted, you'll work for ________. | |
| A. a radio station B. a TV station C. a newspaper office D. a magazine | |
| 3. You may get the position if ________. | |
| A. you have similar working experience B. you can only speak English C. you are good at shooting camera D. you are short of confidence | |
| 4. How can you get in touch with travelogue? | |
| A. By chatting online. B. By posting letters. C. By sending emails. D. By making phone calls. | |
| 5. If you are interested in the job, you must send your CV before ________. | |
| A. May 2 B. May 13 C. May 18 D. May 21 |