1709
Drug repositioning , exemplified by sildenafil and thalidomide , is a promising way to explore alternative indications for existing drugs .
 Chemical: sildenafil; Chemical: thalidomide
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities: sildenafil, thalidomide 
Answer:
 Chemical: sildenafil; Chemical: thalidomide