3909
However , the past few years have demonstrated its role in many biological systems and it is becoming increasingly clear that H2S is likely to join nitric oxide ( NO ) and carbon monoxide ( CO ) as a major player in mammalian biology .
 Chemical: H2S; Chemical: nitric oxide; Chemical: NO; Chemical: carbon monoxide; Chemical: CO
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: H2S; Chemical: nitric oxide; Chemical: NO; Chemical: carbon monoxide; Chemical: CO