南方旧式民居屋顶坡度大,是因为
A:便于接受阳光充足
B:便于空气流通
C:便于散热
D:便于雨水下泻
a.肺泡壁____,由____层上皮细胞构成;
b.肺泡外缠绕丰富的____分析下表数据,与吸入的空气相比,人体呼出的气体中 ____ 的含量减少,____的含量增加。
﹣ The novel seems a little boring.
﹣You won't enjoy it you put your heart into it.