Is it possible for domestic and international passengers to be on the same flight?

The correct answer is that it is indeed possible for domestic and international passengers to be on the same flight under certain regulations. Many airlines operate flights that serve both domestic and international routes, commonly referred to as "transborder" flights.

In these scenarios, the aircraft may depart from a domestic airport and then proceed to an international destination, or vice versa. Regulations set by aviation authorities allow for a mix of passengers, with the understanding that they each comply with their respective travel documentation requirements. For example, international passengers will need to have valid passports and possibly visas, while domestic passengers will typically only require identification as mandated by domestic regulations.

Customs and immigration procedures are generally organized to facilitate the presence of both domestic and international travelers on the same flight. This may include processes for customs checks upon landing at an international destination, ensuring that the regulations governing the entry or departure of international passengers are upheld while also accommodating domestic travelers.

The options suggesting separation of passengers or that it is against airline policy do not align with standard aviation practices or regulations. Airlines strategically run such mixed flights to maximize efficiency and accommodate diverse passenger needs.