You will be given a definition of a task first, then some input of the task.
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: Which of the following answers is true about the HLA molecules?
Options: <1> They are very polymorphic nuclear proteins. <2> They are divided into molecules of class IgG, IgA and IgM. <3> They join peptides and present them on the cell surface. <4> They interact with cytokines to modulate the immune response. <5> They are monomorphic.
Output:
3