Definition: 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: They are directly involved in allergic reactions: 
 Options:  <1> T lymphocytes. <2> Dendritic cells <3> Monocytes <4> Platelets. <5> Mastocytes
