In an attempt to expand viewership of the television show Mystery Science Theater 3000 in its early days, the producers encouraged viewers to make copies of the show on video tapes and give them to friends. The closing credits included the words "Keep circulating the tapes!" This is an example of:
a. guerrilla marketing.
b. cause marketing.
c. ambush marketing.
d. cloud marketing.
Answer: a. guerrilla marketing.