Final answer:
The regulation for mandatory oxygen usage for all persons onboard during a flight is at altitudes above 14,000 feet Above Sea Level (ASL), according to Federal Aviation Regulations.
Step-by-step explanation:
The question "All Persons on board require oxygen for the duration of the flight above __________________ ASL" pertains to aviation regulation regarding the mandatory use of supplemental oxygen. The correct answer is C) 14,000 feet Above Sea Level (ASL). According to Federal Aviation Regulations, specifically FAR 91.211, there are stipulations for the usage of oxygen by crew members and passengers when flying at higher altitudes. For instance, the regulation specifies that when the cabin altitude is above 12,500 feet up to and including 14,000 feet MSL, the minimal flight crew must use supplemental oxygen for periods of flight over 30 minutes. Additionally, at cabin altitudes above 14,000 feet MSL, all occupants must be provided with and use supplemental oxygen continuously.