在0.1 mol/L的Na₂CO₃溶液中，下列关系正确的是(　　)

A．c(Na^＋)＝2c(CO)

B．c(OH^－)＝2c(H^＋)

C．c(HCO)>c(H₂CO₃)

D．c(Na^＋)<c(CO)＋c(HCO)

-- What did your mother say on the phone?

-- She asked _______ .                                           

A. why did I fail the test  B, why I failed the test     C. why did you fail the test