Classify each of the following as an example of direct, interactive, and/or mass marketing.
a. The sales force of a pharmaceutical company visits physicians' offices to promote new medications and to answer physicians' questions about treatment options and possible side effects.
b. A mortgage company targets a list of specific low-risk borrowers for a barrage of e-mail messages touting its low interest rates and fees.
c. An online bookseller pays fees to an Internet search engine to post banner ads relating to each search topic chosen by someone conducting a search. In part, this helps promote the bookseller's brand, but clicking on the banner ad also directs the person to a Web page displaying books on the topic that are available for purchase.
d. A national rental car chain runs advertisements on all of the nation's major television networks.