A Popular Buffer Solution Consists of Carbonate (CO₃²⁻) and Hydrogen

A popular buffer solution consists of carbonate (CO₃²⁻) 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 CO ₃ ²⁻ and 0.1 M HCO ₃ ⁻
B) 0.1 M CO ₃ ²⁻ and 0.9 M HCO ₃ ⁻
C) 0.5 M CO ₃ ²⁻ and 0.5 M HCO ₃ ⁻
D) 0.1 M CO ₃ ²⁻ and 0.1 M HCO ₃ ⁻
E) They all have the same buffer capacity.