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: The class I genes of the Major Histocompatibility Complex:
Options: <1> They are few <2> They are very polymorphic. <3> They express their alleles according to allelic exclusion. <4> They are expressed in all the cells of the organism. <5> They code glycolipids.
A:
2