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.
Input: Question: The classical pathway of complement is activated in response to:
Options: <0> Antigen-antibody complexes. <1> Direct binding of C3b to bacterial walls. <2> Microbial glycolipids. <3> Properdin <4> The C-reactive protein.
Output:
biology