Final answer:
If the jump height is half as high, it generally implies that gravity remains constant because gravity does not change significantly over small distances on Earth. The change in jump height could be due to other factors, not a change in gravity.
Step-by-step explanation:
If the jump height is half as high, this does not necessarily tell us anything about gravity being stronger or weaker without additional context. However, if we assume all other factors are the same and this change in jump height occurs on the same celestial body (like Earth), then it might imply that gravity has remained constant, and the change in jump height could be due to other factors such as the jumper's force or technique.
Considering the principles of gravitational force, we know that it is inversely proportional to the square of the distance from the center of a celestial body (Earth's center, for instance). This means that the further away you are from the center of the Earth, the weaker gravity becomes but only by very small amounts that are often negligible over short distances, such as the height of a building or a jump.
Therefore, if someone's jump height is halved, it can be due to a range of factors, but unless they are jumping on a different planet or a significant distance from Earth's surface, it's unlikely due to a change in gravity. Thus, the correct answer would be c) Gravity remains constant.