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: Histidine and histamine are two compounds with biological importance that have in common as a structural unit: 
 Options:  <1> Pyridine <2> Piperidine <3> Triazine <4> Phenol. <5> Imidazole
