The situation that shows a constant rate of change is the cost of a bunch of grapes compared with its weight.
In this scenario, the cost typically increases at a consistent rate relative to the weight (e.g., a specific price per pound). The other situations may involve variable rates of change due to different factors, such as the height of a bird (which may change unpredictably), or the outside temperature, which can fluctuate throughout the day. The number of tickets sold may also not change at a constant rate as it can depend on various factors leading up to the game.