Task: Text Categorization
Input (English): 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.
Output (English): biology