The company that pays for an ad probably wants certain content in the site. Learn to decipher domain names - see below. Authority - the author has knowledge, credentials. Exercise caution here - anyone can assume any identify on the Internet. Reputable sites tends to link to other reputable sites.
Most companies have a bias, a perspective, something to promote.
The sources on the cart below may be accessed for projects. Unless your teacher specifies, presume you need a variety of sources from a variety of dates. Look for good keywords contained in these articles to use in CD and Internet searches. Books for in depth, generally fair, coverage of subject. Watch out for copyright date if material must be current.