Red blood cells are produced in the body and travel through arteries and
veins to all of the major organs. The
circulatory system is able to maintain
a relatively constant amount of red
blood cells because red blood cells
are regularly produced by -
F the bones of the skeletal system.
G the lymph of the circulatory
system.
H the glands of the endocrine
system.
J the neurons of the nervous
system.

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.