Which alternative energy source is exhaustible? . a) geothermal energy. b) tidal energy. c) solar energy. d) wind energy.

"inexhaustible" is a term that is relative to our lives, and the lives of 10000 generations after us. 

Exhaustible is something that can be used up completely. Everything is exhaustible except solar power, wind power, tidal and wave power. 

Exhaustible is anything that we find under the ground. Thermal power comes from deep under the earth. The dynamo that is our earth's core will eventually quit producing usable heat for those ancestors of ours and will likely go the way of mars, a geographically dead planet that no longer has the ability to re-shape its surfaces through its own core's energy. 

Anything that we find under the ground.C.Geothermal Energy