Final answer:
The conditioned stimulus in the scenario is the car, as it becomes associated with the hot women, which initially elicit a positive response of attraction or desire.
Step-by-step explanation:
In the context of advertising and associative learning, the conditioned stimulus refers to a previously neutral stimulus that, after becoming associated with an unconditioned stimulus, gains the power to elicit a conditioned response. In the scenario described where straight guys are more likely to buy a car after viewing an advertisement with hot women sitting on the cars, the hot women are used to create a positive emotional response. Thus, when the presence of these women becomes associated with the car, the car becomes a conditioned stimulus as it starts to evoke attraction or desire which was initially elicited solely by the women themselves.