Swimming in water is possible due to Newton’s third law of motion. This law states that for every action, there is an equal and opposite reaction. When a swimmer pushes against the water with their arms and legs (action), the water pushes back with an equal and opposite force (reaction). This reaction force propels the swimmer forward through the water. Newton’s first law of motion, also known as the law of inertia, describes the tendency of objects to remain at rest or in uniform motion unless acted upon by an external force. Newton’s second law of motion relates force, mass, and acceleration, describing how the force applied to an object affects its motion. While both laws are relevant in understanding swimming mechanics, it is primarily Newton’s third law that directly explains the propulsion achieved by swimmers through action and reaction forces with the water. Therefore, the correct answer is [C] Third law.