Detailed Instructions: In this task, you are given a question and answer options for that question. Using this information, you have to classify each text into different topics: medicine, nursery, psychology, chemistry, pharmacology, biology.
Problem:Question: The so-called poly-Ig receptor: 
 Options:  <0> Facilitates the transport of IgA through the mucosal epithelium. <1> Mediates the transport of IgG through the placenta. <2> Stabilizes the polymer structure of an IgM. <3> It is expressed on the surface of B lymphocytes. <4> It is expressed on the surface of tissue macrophages.
Solution:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
biology