When considering the concept of scarcity in decision-making for fundraising, the members should focus on resource allocation and demand for their chosen method. Among the options you've presented, "Is there enough consumer demand for a car wash?" is the most relevant thought to guide their decision-making process.
This approach examines whether there is sufficient demand for the car wash services, which relates to the scarcity of customers and their willingness to pay for the service, thus affecting potential revenue. If demand is high, the car wash could be a successful fundraising activity.
While the other questions are important to consider—such as storage of unsold energy drinks (to avoid waste), the availability of the concession stand, and the need for enough volunteers—understanding consumer demand directly influences the success of the fundraising effort based on available resources.