17399
Reactive oxygen and nitrogen species ( ROS and RNS ) are continuously produced in the cellular systems and are controlled by several antioxidant mechanisms .
 Chemical: oxygen; Chemical: nitrogen
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: oxygen; Chemical: nitrogen