If gravity is the ONLY force acting on an object, that's when we say the object is in "<em>free fall</em>".
Since the y axis stayed consistent, we can assume it did not move at all.
(So your answer would be A)
1. A spring or elastic can be stretched to store energy as it wants to return to rest.
2. Gravitational every can be is stored by moving a ball against gravity when lifted then released when bounced.
3. Separating two charged plates will store energy as the plates want to return to their original position.
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