检测水样中"三氮",在采样前应在采样容器中加入的水质保存剂是

A、H[img=~/QImg/2013-10-14-11-46-19/image002.jpg]SO[img=~/QImg/2013-10-14-11-46-19/image004.jpg]
B、Na[img=~/QImg/2013-10-14-11-46-19/image002.jpg]CO[img=~/QImg/2013-10-14-11-46-19/image003.jpg]
C、NaHCO[img=~/QImg/2013-10-14-11-46-19/image003.jpg]
D、Na[img=~/QImg/2013-10-14-11-46-19/image002.jpg]SO[img=~/QImg/2013-10-14-11-46-19/image004.jpg]
E、NaCl