-How Does Doubling the Concentration of the Alkyl Halide in Br

$$\mathrm { CH } _ { 3 } \mathrm { Br } + \mathrm { HO }^ { \ominus } \longrightarrow \mathrm { CH } _ { 3 } \mathrm { OH } + \mathrm { Br }^ { \ominus }$$
-How does doubling the concentration of the alkyl halide in the above S_N2 reaction affect the rate of the reaction?

A) no change
B) doubles the rate
C) triples the rate
D) quadruples the rate
E) rate is halved