Acircuit is a. a switch that interrupts an electric current. b. the incomplete path of an electrical current. c. the complete path of an electrical current. d. an open path of an electrical current.

In order for a circuit to function, it must have a complete and connected path on which an electrical current (electrons) can travel. Electrons cannot travel over a break in the path.
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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.