Wingtip vortices are created only when an aircraft is:

Wingtip vortices are a byproduct of the lift generated by an aircraft's wings. When an aircraft is in flight, airflow over the wings creates an area of lower pressure above the wing and a higher pressure below it. This pressure difference results in the air from underneath the wing flowing around the wingtips and spilling over to the upper surface, creating swirling vortices of air that trail behind the aircraft.

These vortices form whenever an aircraft is generating lift, which typically occurs during various phases of flight, such as takeoff, cruising, and landing—not just under specific conditions like climbing or descending. Therefore, the correct response highlights that wingtip vortices are indeed produced when lift is being developed, regardless of whether the aircraft is climbing, cruising straight and level, or in any other phase where lift is generated.

By recognizing that lift must be present for vortices to form, it becomes clear how essential lift is in relation to understanding the aerodynamic effects around an aircraft in flight.