Which of the Following Undergoes a Substitution Reaction with Sodium $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{~F}$

Which of the following undergoes a substitution reaction with sodium cyanide in DMSO at the fastest rate?

A) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{~F}$
B) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}$
C) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br}$
D) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{I}$