Reactivity of following on the basis of $\mathrm { S } _ { \mathrm { N } } 1$ mechanism.
(I) [structure 1]
(II) [structure 2]
(III) [structure 3]
(IV) [structure 4]
(A) $\mathrm { I } > \mathrm { II } > \mathrm { III } > \mathrm { IV }$
(B) II $>$ I $>$ III $>$ IV
(C) IV $>$ II $>$ III $>$ I
(D) IV $=$ II $>$ III $>$ I