3943
When both skin test and RAST for BPO were negative , single - blind , placebo - controlled challenge tests were done to ensure tolerance of PG or sensitivity to AX .
 BPO, PG, AX
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Disease, Chemical 
Text: {0} 
Answer:
 BPO, PG, AX