The increasing order of reactivity of the following halides for the `S_(N^(1))` reaction is :
`CH_(3)-underset(CI)underset(|)(CH)-CH_(2)CH_(3) " " underset((II))(CH_(3)CH_(2)CH_(2)CI)`
`underset((III))(p-H_(3)CO-C_(6)H_(4)-CH_(2)CI)`
A. `III lt II lt I`
B. `II lt I lt III`
C. `I lt III lt II`
D. `II lt III gt I`