Definition: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Input: Question: What is a prodrug? 
 Options:  <1> A drug of series of a therapeutic class. <2> A drug that has been withdrawn from the market. <3> An inactive product that is enzymatically converted to an active drug. <4> A compound of natural origin from which one or more drugs are obtained by hemisynthesis. <5> A drug that lacks activity but enhances the action of others.
