既能增强神经肌肉兴奋性,又能降低心肌兴奋性的离子是( )

A、CA[img=~\/QImg\/2013-06-26-17-11-54\/image019.gif]
B、Mg[img=~\/QImg\/2013-06-26-17-11-54\/image019.gif]
C、H[img=~\/QImg\/2013-06-26-17-11-54\/image020.gif]
D、OH[img=~\/QImg\/2013-06-26-17-11-54\/image018.gif]
E、K[img=~\/QImg\/2013-06-26-17-11-54\/image020.gif]