http://www.nytimes.com/2015/05/04/business/energy-environment/the-uphill-battle-to-better-regulate-formaldehyde.html?_r=0
http://www.cancer.org/cancer/cancercauses/othercarcinogens/intheworkplace/formaldehyde
http://www.cancer.gov/about-cancer/causes-prevention/risk/substances/formaldehyde/formaldehyde-fact-sheet
use this articles to finish the assignment