下列哪个公式可出现负值

A、[img=~/QImg/2013-10-14-11-12-39/image005.jpg]
B、[img=~/QImg/2013-10-14-11-12-39/image006.jpg]
C、[img=~/QImg/2013-10-14-11-12-39/image007.jpg]
D、[img=~/QImg/2013-10-14-11-12-39/image008.jpg]
E、[img=~/QImg/2013-10-14-11-12-39/image009.jpg]