Which Substrate Will Undergo the Reaction the Fastest $\mathrm { RBr } \stackrel { \mathrm { NaOCH } _ { 3 } } { \longrightarrow } \mathrm { ROCH } _ { 3 } + \mathrm { NaBr }$

Which substrate will undergo the reaction the fastest?
$\mathrm { RBr } \stackrel { \mathrm { NaOCH } _ { 3 } } { \longrightarrow } \mathrm { ROCH } _ { 3 } + \mathrm { NaBr }$

A) compound A
B) compound B
C) compound C
D) compound D