Human babies have a gene that produces an enzyme that breaks down the sugar found in milk. Over time, this gene is shut off in most adult humans. A mutation in this gene allows some adults to continue to drink milk without discomfort. Why would this mutation have allowed early humans to survive?.

Which source would provide the most bias-free information about smoking and increased health risks? a) a website created by heart disease patients b) a research study conducted by the mayo clinic eliminate c) a public service message sponsored by tobacco companies d) an online question forum conducted by attorneys for cardiac specialists