Which Base Listed Below Would Be the Strongest Given the Corresponding

Which base listed below would be the strongest given the corresponding acid ionization constants for their conjugate acids?

A) PO₄^{3 -} ; K _a(HPO₄^{1 -} ) = 4.2×10 ^{- 13}
B) NO₂^{1 -} ; K _a(HNO₂) = 7.1×10 ^{- 4}
C) HCO₃^{1 -} ; K _a(H₂CO₃) = 4.5×10 ^{- 7}
D) CH₃COO^{1 -} ; K _a(CH₃COOH) = 1.8×10 ^{- 5}
E) F ^- ; K _a(HF) = 6.8×10 ^{- 4}