Rank from most basic to least basic:
a) HC₂⁻ > I⁻ > CH₃NH⁻ > HS⁻
b) I⁻ > HS⁻ > HC₂⁻ > CH₃NH⁻
c) HS⁻ > CH₃NH⁻ > I⁻ > HC₂⁻
d) CH₃NH⁻ > HC₂⁻ > HS⁻ > I⁻