Given the following conjugate acid-base pairs and their Ka values at 25°C, which of the following acid-base buffer systems might be found in the human body (near pH 7)?
a. HCO₃⁻/CO₃²⁻; Ka = 4.7x10⁻¹¹
b. C₆H₅COOH/C₆H₅COO; Ka = 6.20x10⁻⁵
c. H₂PO₄²⁻/HPO₄⁻; Ka = 6.4x10⁻⁸
d. H³PO₄/H₂PO₄²⁻; Ka = 6.9x10⁻³
