15854
In this study we have conducted a comparative analysis of the toxicity of perfluorinated carboxylic acids ( PFCA ) with a carbon chain length ranging from four to twelve carbon atoms .
 perfluorinated carboxylic acids, PFCA, carbon, carbon
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 perfluorinated carboxylic acids, PFCA, carbon, carbon