草酸(H₂C₂O₄)是二元弱酸，KHC₂O₄溶液呈酸性。向100mL0.2mol/L的草酸溶液中加入1.68 g KOH固体，若溶液体积不变，则对所得溶液中各粒子浓度之间的关系描述正确的是

A．c(C2O4^2^－)＋c(HC2O4^－)＋c(OH^－)＝c(K^＋)＋c(H^＋)

B．c(C2O4^2^－)＋c(HC2O4^－)＋c(H2C2O4)＝0.2mol/L

C．c(C2O4^2^－)＜c(HC2O4^－)＜c(H2C2O4)

D．c(H^＋)＜c(HC2O4^－)＜c(C2O4^2^－)＜c(K^＋)