Answer:
C. lighter-than-air aircraft
Explanation:
A multirotor is a rotorcraft with more than two lift-generating rotors. An advantage of multirotor aircraft is the simpler rotor mechanics required for flight control. Â Multirotor drones are used by hobbyists so it could be recreational, but mostly it's used in radio control aircraft so not recreational. It's unmanned so it's not b. If not a or b it has to be c or d. Most of it's airborne time is it being lighter-than air. I'd choose c.
