Which of the following print-media pieces has the most credibility?
Select one:
a. a billing insert from a bank, featuring photos and information about several vacation packages and offering discounts with use of the bank's credit card
b. an environmental magazine featuring many articles and pictures of a healthy planet, paid for by an association of oil and gas companies
c. a brochure explaining how oil helps engines run, sponsored by a company called We Win You Lube
d. a brochure provided by a pharmacist, outlining dosage information and potential side effects of a particular medicine