18511
Phosphodiesterase type 5 inhibitors ( PDE5 - Is ) improve cognitive performance of rodents , but the few human studies investigating their effects did not systematically investigate cognitive effects and the results have been quite contradictory .
 None
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:  
Answer:
 None