下列公式中哪一个能用来精确地计算任意浓度[c(HCl)]的HCl水溶液中氢离子浓度
[c(H⁺)](K_w为水的离子积常数)                                                                        （   ）                                           

A．c(H^+)="c(HCl)"	B．c(H^+)=c(HCl)+Kw/c(H^+)
C．c(H^+)=c(HCl)+Kw	D．c(H^+)=c(HCl)−Kw/c(H^+)