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: The majority of regulatory T lymphocytes express high levels of:
Options: <1> Molecules of the B7 family. <2> CD8. <3> The alpha chain of the receptor for IL-2. <4> IL-17. <5> Perforin
Output:
3