题目内容：

区分下列各组物质的两种方法都正确的是

              需区分物质                                方法一                                                  方法二

A           空气和氧气                                用带火星木条检验                             闻气味

B            硬水和软水                                观察颜色                                              加明矾搅拌

C            铜丝和铁丝                                用磁铁吸引                                          观察颜色

D           二氧化碳和氮气                       澄清石灰水                                          燃着的木条