In the acid-base mechanism, the base is a proton acceptor, and the acid is the proton donor. An acid-base reaction is visualized as the reaction in which proton transfer takes place. However, in a nucleophilic substitution reaction, the nucleophile attacks a substrate (usually an electrophile), and the leaving group is removed from the substrate as a weaker nucleophile. The nature of the reactants determines whether a reaction will proceed as an acid-base reaction or a nucleophilic substitution reaction. Classify each reaction as a nucleophilic substitution reaction or an acid-base reaction.

a. CH3CH2O-+CH3Br → CH3CH2OCH3+Br-
b. CH3CH2OH+HCl → CH3CH2Cl+H2O
c. CH3COOH+NaOH → CH3COONa +H2O
d. CH3CH2CH2Br+HCN→CH3CH2CH2CN+HBr
e. CH3CH2OH+KOH→CH3CH2OK +H2O