Final answer:
The main input for an airline is passengers, who are the primary revenue source for airlines. While other inputs such as airplanes, customs agents, and crew are important, the presence of these inputs is contingent upon the presence of passengers. Option A
Step-by-step explanation:
The main input for an airline is passengers. Passengers are the primary revenue source for airlines, as they pay for tickets to travel on airplanes. Without passengers, airlines would not have any business.
Airlines also rely on other inputs such as airplanes (the vehicles used for air travel), customs agents (for international flights to facilitate customs and immigration processes), and crew (pilots, flight attendants, etc.) who operate the airplanes and provide services to passengers. However, the presence of these inputs is contingent upon the presence of passengers.
In summary, while airplanes, customs agents, and crew are important inputs for airlines, the main input is passengers. Option A