-How Does Doubling the Concentration of the Alkyl Halide Affect

$\left(\mathrm{CH}_{3}\right) _{3} \mathrm{CBr}+\mathrm{I}^{\ominus} \longrightarrow\left(\mathrm{CH}_{3}\right) _{3} \mathrm{CI}+\mathrm{Br}^{\ominus}$

-How does doubling the concentration of the alkyl halide affect the rate of the above S_N1 reaction?

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