图为肺的内部结构示意图，图中所示肺泡外包围着毛细血管，肺泡壁和毛细血管壁都很薄，由一层上皮细胞构成，这有利于（  ）

读“北美大陆沿40°N地形剖面图”，判断A山脉是：

从行为获得的途径来看，下列动物行为属于学习行为的是（　　）

   Mr Smith 1from London. Now he is in China. He is 2 .He teaches 3 a middle school. He works very hard. His students like 4 very much. He can 5 a little Chinese . His students often teaches him Chinese 6 Sundays. Mr Smith likes playing football . He often plays football 7 his students.
   Mr Smith8  a son. His name is Jack. He is student. He studies in a middle school. He goes to school  9 bike everyday. He gets back home at four in the afternoon. He likes 10 TV in the evening.