2729
Ritanserin is a new substance with highly selective blocking activity on S2 receptors for 5 - HT in the central nervous system .
 GENE: S2 receptors
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: GENE 
Text: {0} 
 Entities: S2 receptors 
Answer:
 GENE: S2 receptors