In which of the following pair one species is incorrectly indicated which would give higher Substitution /Elimination ratio when it reacts with isopropyl bromide.

Question

$$\begin{array}{1 1}(a)\;EtO^-\;or \;tBuO^-\\(b)\;Cl^-\;or\;Br^-\\(c)\;OCN^-\;or \;SCN^-\\(d)\;CH_3S^-\;or \;CH_3O^-\end{array}$$