Which of the following must be part of the pre-takeoff check?

The correct answer focuses on assuring compliance with the holdover time as part of the pre-takeoff check, which is critical for ensuring flight safety in certain weather conditions. Holdover time refers to the length of time after de-icing or anti-icing fluid has been applied during which the aircraft can remain on the ground without being recontaminated by ice, snow, or frost.

This is particularly essential under colder or adverse weather conditions where ice accumulation can compromise the aircraft's performance and safety. By ensuring compliance with holdover times, the flight crew can ascertain that the aircraft is safe for takeoff and that necessary de-icing procedures have effectively protected the aircraft surfaces.

While checking passenger safety equipment and reviewing flight destinations are certainly important aspects of flight preparation, they do not have the same immediate impact on the safety and operation of the aircraft during adverse weather conditions as holdover times do. Confirming the availability of refreshments, while it may enhance passenger comfort, is not a critical safety-related procedure and therefore does not fall under the mandatory pre-takeoff checks.