Fitness is a medical term describing the effect of exercise on body systems and disease prevention.

Physical fitness is a medical term describing the effect of exercise on body systems and disease prevention. The body’s ability to function efficiently and effectiveness' it should contain health-related physical fitness and skill-related physical fitness. Physical fitness includes metabolic fitness and bone integrity. It is associated with person’s ability to resist hypokinetic diseases.

Optimal physical fitness is not possible without regular exercise.

The answer is atmosphere. there are four spheres of the earth: 1. geosphere (from greek word 'geo' = ground), 2. hydrosphere (from greek word 'hydro' = water), 3. biosphere (from greek word 'bio' = life), and 4. atmosphere (from greek word 'atmo' = air). a magnetosphere is a region of space around astronomical objects controlled by the magnetic field of that object. through the process of elimination, since lightning is present in the air, it can be found in the atmosphere.

Exposure to solar flares would be the correct answer