Which One of the Following Monomers Undergoes Cationic Polymerization Most $\mathrm{H}_{2} \mathrm{C}=\mathrm{CH}_{2}$

Which one of the following monomers undergoes cationic polymerization most readily?

A) $\mathrm{H}_{2} \mathrm{C}=\mathrm{CH}_{2}$
B) $\mathrm{H}_{2} \mathrm{C}=\mathrm{CHCH}_{3}$
C) $\mathrm{H}_{2} \mathrm{C}=\mathrm{C}\left(\mathrm{CH}_{3}\right) _{2}$
D) $\mathrm{H}_{2} \mathrm{C}=\mathrm{CHCN}$