Final answer:
The sharpness of a large vehicle's turn is determined by the turning radius of the front wheels and the amount of off track of the rear wheels.
Step-by-step explanation:
The two factors that determine the sharpness of a large vehicle's turn are the turning radius of the front wheels and the amount of off track of the rear wheels.
The turning radius of the front wheels refers to how tightly the front wheels can rotate, with a smaller turning radius allowing for sharper turns.
The amount of off track of the rear wheels refers to the distance between the rear wheels and the path that the front wheels take, with a larger off track resulting in a wider turn.
Therefore, the correct answer is d. a and b.