1891
The present study evaluated the in vitro mechanisms of AgNP ( < 100 nm ) toxicity in relationship to the generation of reactive oxygen species ( ROS ) in A549 cells .
 Chemical: oxygen
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