21128
Hydrogen sulfide ( H2S ) is a toxic gaseous substance , and accidental exposure to high concentrations of H2S has been reported to be lethal to humans .
 Chemical: Hydrogen sulfide; Chemical: H2S; Chemical: H2S
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: Hydrogen sulfide; Chemical: H2S; Chemical: H2S