Instructions: 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: Which coenzyme acts as an inhibitor of the citric acid cycle (or tricarboxylic acid cycle):
Options: <1> Lipoic acid. <2> Ascorbic acid. <3> Biocytin. <4> Coenzyme Q. <5> NADH + H +.
Output:
5