C + D.
The rate law for the reaction is expressed as rate = k [A]m [B]n
If the concentration of B is kept large, then [B] essentially does not change over time and if the rate of reaction is determined as rate = k [A] then this reaction is a pseudo first order reaction. Acidic hydrolysis of ethyl acetate is an example of a first order reaction, where the acid concentration is kept in excess in the solvent, water.