Looking at the answer options:

is produced when a helicopter hovers, or an aeroplane is creating lift --> CORRECT. See below for more information.

only occurs once an aircraft is clear of the ground --> INCORRECT. The vortices commence when the nose wheel lifts off on rotation.

commences when the main gear of a departing aeroplane leaves the runway --> INCORRECT. The vortices commence when the nose wheel lifts off on rotation.

is not a helicopter phenomenon --> INCORRECT. Helicopters do indeed create wake turbulence, see below for more information.

WAKE TURBULENCE

Whenever an aeroplane generates lift, air spills over the wing tips from the high pressure areas below the wings to the low pressure areas above them. This flow causes rapidly rotating whirlpools of air called wingtip vortices. An aircraft generates vortices from the moment it rotates on take-off to touchdown.

Pilots should be particularly alert in calm wind or light winds of 3 to 7 knots conditions and where the vortices could stay in the touchdown area, sink into your take-off or landing path, or drift over a parallel runway. Calm wind conditions are most dangerous as wake turbulence stagnates on the runway and is not blown to one side.

In a slow hover taxi or stationary hover near the surface, helicopter main rotor(s) generate downwash producing high velocity outwash vortices to a distance approximately three times the diameter of the rotor. When rotor downwash hits the surface, the resulting outwash vortices have behavioural characteristics similar to wing tip vortices produced by fixed wing aircraft. However, the vortex circulation is outward, upward, around, and away from the main rotor(s) in all directions. Pilots of small aircraft should avoid operating within three rotor diameters of any helicopter in a slow hover taxi or stationary hover. In forward flight, departing or landing helicopters produce a pair of strong, high-speed trailing vortices similar to wing tip vortices of larger fixed wing aircraft. Pilots of small aircraft should use caution when operating behind or crossing behind landing and departing helicopters.