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: With what scope is the Theory of the Melzack Gate and Wall related ?: 
 Options:  <0> Cancer. <1> HIV infection <2> Renal problems. <3> Pain. <4> Cardiovascular disorders
Output:
psychology