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: The most abundant immunoglobulin isotype produced by plasma cells of mucosal-associated lymphoid tissue is: 
 Options:  <1> IgM <2> IgD. <3> IgG <4> IgA <5> IgE
