Final answer:
On a graph with Speed on the x-axis and Height on the y-axis, the option that correctly describes the relationship would be 'As speed increases, height decreases', portraying a negative slope or negative relationship between these two variables.
Step-by-step explanation:
When analyzing how two variables are related on a graph, where one is plotted on the x-axis and the other on the y-axis, we are examining the relationship between them.
With Speed on the x-axis as the independent variable and Height on the y-axis as the dependent variable, if the graph shows a straight-line relationship similar to the altitude-air density relationship with a negative slope, then when Speed (x) increases,
Height (y) decreases, and vice versa.
The correct answer, based on the description of a negative slope, would therefore be Option C, which states 'As speed increases, height decreases'.
This implies a graph with a downward trend as we move from left to right, demonstrating a negative relationship between speed and height.