Correct statement regarding $S_{N}2$ reaction is

A) rate = K[Substrate] [Nu]

B) Stronger nucleophiles cause faster rate

C) Favored by aprotic solvents

An S_N2 reaction is a bimolecular nucleophilic substitution reaction, which means there is only one step. In this step, both the nucleophile and the substrate are involved.

For S_N2 reaction, nucleophile is one of the rate-determining factors, therefore strong nucleophile helps to speed up S_N2 reactions. 

The rate of S_N2 reaction is maximum when the solvent is polar aprotic such as DMSO (dimethyl sulphoxide) (CH₃​)₂​S→O. In such solvents, the nucleophile is not solvated and can freely attack the substrate. Also, the polar nature of the solvent helps in the cleavage of C−X bond where X is the leaving group.