A group which departs from the substrate in a nucleophilic substitution reaction is called a leaving group. The ease of departure is determined by the acidity of the conjugate acid of the leaving group; higher the acidity, better the leaving group. The correct order of reactivity of the following compounds in a given nucleophilic reaction is

A

$$\mathrm{R-Cl > R-OCOCH_3 > R-OSO_2CH_3 > RI}$$

B

$$\mathrm{R-OSO_2CH_3 > R-Cl > R-OCOCH_3 > ROH}$$

C

$$\mathrm{R-I > RNH_2 > R-OCOCH_3 > R-OSO_2CH_3}$$

D

$$\mathrm{R-Br > R-OSO_2CH_3 > R-OCOCH_3 > ROCH_3}$$