If you "close" your elbow bringing your forearm to rest against your upper arm, then your elbow is exhibiting:

 By "closing" the elbow, we are exhibiting flexion.

The act of flexing or bending a joint, in this case the elbow, is to approximate the parts it connects to. This action is possible because of the muscles around the joint, called the flexors (Brachialis, Brachioradialis and Biceps brachii muscle)

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.