The label that corresponds to the segment showing the balloon descending but not landing is C.
In the given description:
- Segment A is increasing, indicating the balloon is rising.
- Segment B is constant, meaning the balloon is at a steady height.
- Segment C is decreasing, which indicates that the balloon is descending.
- Segment D is also constant, meaning the balloon remains at a steady height again.
Since you are looking for the segment indicating the balloon is descending, segment C is the correct choice.