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'.
Q: Question: Pyridazine is an aromatic heterocycle that contains in its structure:
Options: <1> A nitrogen <2> Two nitrogens <3> Three nitrogens <4> Four nitrogens <5> No nitrogen
A:
2