下表中列出了一些物质的熔点和沸点（1标准大气圧下），根据表中数据回答下列问题：

物质	熔点（℃）	沸点（℃）
水	0	100
萘	80	210
水银	-39	357
酒精	-117	78
氮	-210	-196
氧	-268	-183

（1）表中所列物质在常温下属于固态的是________；氧在-145℃时所处的状态是______
（2）要探究萘的熔化和沸腾过程中温度的变化，应选_______作温度计的测量物质。
（3）如果在1标准大气压下用降温的办法从空气中提取氧和氮，那么温度下降时首先液化被分离出来的是                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  （4）1标准大气圧下，当温度为0℃时，水的状态（  ）
A．一定是固态    　       B．一定是液态    　 
C．一定是固液共存态      　D．以上三种状态都有可能