Despite a general decline in sales of other eco-friendly vehicles, the EcoDrive is experiencing a surge in popularity. The manufacturers of the EcoDrive claim that this success is due to its competitive pricing and exceptional fuel efficiency. However, since the EcoDrive's price and fuel efficiency are similar to those of its rivals, it is more plausible that its popularity stems from consumers' desire to be seen as environmentally responsible by their peers. Which one of the following is an assumption required by the argument?