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We sequentially exposed cells to air - delivered copper ( Cu ) NPs in vitro to compare toxicity results to our prior in vivo inhalation studies .
 Chemical: copper; Chemical: Cu
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: copper; Chemical: Cu