Selection C is appropriate.
Probably, the function only usefully describes the height between the time it is thrown (x=0) and the time it lands (x=5).
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Conceivably, a function can be written that would describe height before it is thrown and after it hits the ground (as after it bounces, for example). In that case, one might be interested for the domain of "all real numbers" or at least "all real numbers representing the time during which the object was in existence."
