Final answer:
The subject of this question is Physics, and the action being described is a jackknife dive.
Step-by-step explanation:
The described dive, where you bend in midair to touch the toes while keeping the legs straight and then straighten the body, is known as: c) Jackknife. A jackknife dive is a specific diving technique characterized by the described sequence of movements. In this dive, the diver starts by bending at the waist, bringing the upper body and legs together to touch the toes while maintaining straight legs. After this initial position, the diver then straightens the body before entering the water. The jackknife dive is one of the fundamental dives in competitive and recreational diving, requiring control, flexibility, and precision in execution. Options a (Somersault), b (Backflip), and d (Plunge) describe different types of dives with distinct movements and positions.