Which Anionic Base Listed Below Would Be the Strongest Given

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

A) F ^- ; K _a(HF) = 6.8×10 ^{- 4}
B) CH₃COO ^- ; K _a(CH₃COOH) = 1.8×10 ^{- 5}
C) IO₃^{1 -} ; K _a(HIO₃) = 1.6×10 ^{- 1}
D) NO₂^{1 -} ; K _a(HNO₂) = 7.1×10 ^{- 4}