Final answer:
The Curiosity Rover used the sky crane maneuver to land on the surface of Mars, which involved a hovering descent stage lowering the rover gently onto the surface after being slowed by a parachute and retro-rockets.
Step-by-step explanation:
The Curiosity Rover landed on Mars using an unconventional method because of its size, the complex terrain of the landing site, and its precise landing requirements. The correct landing method used by the Curiosity Rover is option c) it was airlifted and gently placed on the surface by a hovering spacecraft. This innovative system, known as the sky crane maneuver, involved a parachute and retro-rockets to slow down the descent, but instead of landing on its wheels, the rover was lowered down using a tether from the descent stage that acted as a sky crane. This method was necessary to ensure a safe landing in the Gale crater, which had been selected for its complex geology and signs of ancient water.
Previous Mars missions had used simpler landing techniques involving airbags to cushion the landing because they were lighter and the landing sites were flatter. Curiosity's sheer size, its pursuit of more advanced scientific goals, and the hazardous terrain of Gale crater warranted the development and use of the sky crane system.