Option 1: The athlete`s linear momentum refers to the product of the athlete`s mass and velocity, and it is not constant during the fall. As the athlete performs exercises in the air, their velocity will change, affecting their linear momentum. Therefore, option 1 is incorrect.

Option 2: The athlete`s moment of inertia refers to the resistance of an object to changes in its rotation. During the fall, the athlete does not experience any external torques that would change their moment of inertia. However, as the athlete rotates or changes their body position, their moment of inertia can change. Therefore, option 2 is not the correct answer.

Option 3: The athlete`s kinetic energy refers to the energy of the athlete due to their motion. As the athlete performs exercises in the air, their velocity and position will change, affecting their kinetic energy. Therefore, option 3 is incorrect.

Option 4: The athlete`s angular momentum refers to the product of the athlete`s moment of inertia and angular velocity. During the fall, the athlete does not experience any external torques that would change their angular momentum. The athlete`s angular velocity might change as they rotate or change their body position, but their moment of inertia remains constant. Therefore, option 4 is the