— ________.
A:He is at home
B:He is in his room
C:Yes,they are
D:I don't know
在进行“氧气的实验室制取与性质”实验时,某同学制得的氧气不纯.你认为可能的原因是( )
读我国南方地区图(如图),完成下列各题.