Rank the following acids' conjugate bases in terms of their strength as a base. Acid Kₐ:
a) CH₃COOH, 1.8 × 10⁻⁵
b) HNO₂, 4.5 × 10⁻⁴
c) HCOOH, 1.7 × 10⁻⁴
d) HCN, 4.9 × 10⁻¹⁰