Given the task definition and input, reply with output. 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'.

Question: The denaturing of proteins:
Options: <1> Alters the native conformation without affecting the biological activity. <2> It is always irreversible. <3> It can only be achieved by treatment with strong acids. <4> It does not affect the primary structure. <5> It produces the hydrolysis of the protein.
4