Which of the Following Alkyl Halides Is the Least Reactive $\left( \mathrm { CH } _ { 3 } \right) _ { 3 } \mathrm { CCH } _ { 2 } \mathrm { I }$

Which of the following alkyl halides is the least reactive in an E2 reaction?

A) $\left( \mathrm { CH } _ { 3 } \right) _ { 3 } \mathrm { CCH } _ { 2 } \mathrm { I }$
B) $\left( \mathrm { CH } _ { 3 } \right) _ { 2 } \mathrm { CHCHICH } _ { 3 }$
C) $\left( \mathrm { CH } _ { 3 } \right) _ { 2 } \mathrm { CHCH } _ { 2 } \mathrm { Br }$
D) $\left( \mathrm { CH } _ { 3 } \right) _ { 2 } \mathrm { CHCH } _ { 2 } \mathrm { Cl }$
E) $\left( \mathrm { CH } _ { 3 } \right) _ { 2 } \mathrm { CHCH } _ { 2 } \mathrm { CH } _ { 2 } \mathrm { Cl }$