Many Hollywood movie stars were among the first to buy electric and hybrid vehicles. These stars often became __________, influencing other consumers' behavior.

The correct answer is reference groups. In consumer behavior, reference groups are individuals or groups that significantly influence an individual's attitudes, beliefs, or behaviors. Hollywood movie stars, given their visibility and societal impact, often serve as role models or points of reference for the general public. When these stars adopt electric and hybrid vehicles, they promote these products not just through direct endorsements, but by setting an example that others may follow.

Consumers often look to reference groups for cues on what to purchase based on the belief that these individuals or groups are credible and embody certain desirable traits, like being environmentally friendly in the case of electric and hybrid vehicles. This creates a ripple effect where their choices can sway public opinion and consumer behavior, leading to a greater acceptance and interest in these alternative vehicle options.

The other choices, while related to marketing concepts, do not accurately describe the influence that the Hollywood stars exert in this context. Price leaders typically refer to firms or products that set a price standard in a market. Market segments are groups of consumers defined by shared characteristics, and promotional influencers, while similar to the idea of celebrities promoting products, do not capture the specific social influence dynamic that comes from reference groups.