A Popular Buffer Solution Consists of Carbonate (CO₃^2-) and Hydrogen

A popular buffer solution consists of carbonate (CO₃^2-) and hydrogen carbonate (HCO₃^-) conjugate acid-base pair. Which, if any, of the following such buffers has the highest buffer capacity?

A) 0.9 M CO₃^2- and 0.1 M HCO₃^-
B) 0.1 M CO₃^2- and 0.9 M HCO₃^-
C) 0.5 M CO₃^2- and 0.5 M HCO₃^-
D) 0.1 M CO₃^2- and 0.1 M HCO₃^-
E) They all have the same buffer capacity.