To Simulate the PH of Blood, Which Is 7 $\times$ 10^-8) and Disodium Hydrogen Phosphate (K_a = 3

To simulate the pH of blood, which is 7.4, an undergraduate researcher in a biology lab produced a buffer solution by dissolving sodium dihydrogen phosphate (K_a = 6.2 $\times$ 10^-8) and disodium hydrogen phosphate (K_a = 3.6 $\times$ 10^-13) together in an aqueous solution. What mole ratio of Na₂HPO₄/NaH₂PO₄ did she need to use?

A) 1.2
B) 1.6
C) 0.90
D) 1.0
E) 0.96