Amy designed an experiment to test how exercise affects adult men. The resting heart and respiratory rates were measured in fifty men between the ages of 25-55. Once a baseline was established, the men were asked to run on the treadmill for five minutes. The breathing rate and heart rate were recorded every thirty seconds. A graph of her results is below.

What can be inferred from the results of Amy's experiment?
A.
There is no apparent relationship between exercise and heart rate.
B.
There is no apparent relationship between heart rate and respiratory rate.
C.
An increase in heart rate correlates with a decrease in respiratory rate.
D.
There is a positive correlation between heart rate and respiratory rate.