21. formed from both endoderm and ectoderm: a. pharathryoid glands

b. pharyngeal groove

c. pharyngeal pouch

d. thymus

e. tympanic membrane

22. nephron development begins with migration of cells from around uretric bud tip to region of the uretric stalk. these cells differentiate to form the

a. renal cortex

b. renal vesicle

c. renal pyramid

d. penal papilla

e. renal pelvis

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.

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