下列物质中,不属于金属材料的( )
A:钢
B:铝
C:氧化铁
D:18K黄金
体育课剧烈运动后,呼出的气体和吸入的气体相比,含量明显增加的气体是( )
—Chongqing is ____________ than ____________ city in the north of China.
—I think so. It's the hottest city ____________ the southwest of China.