The graph represents a person’s heart rate in beats per minute during 30 minutes of exercise.

A graph titled Cardiac Exercise. The horizontal axis shows time (minutes), numbered 3 to 30, and the vertical axis shows Heart Rate (b p m) numbered 15 to 150. The line starts at 75 b p m in 0 minutes, to 135 b p m from 6 to 25 minutes, and ends at 105 b p m at 30 minutes.

Which statement best describes the relationship between heart rate and time during exercise?

The heart rate increases for 6 minutes, remains constant for 19 minutes, and then gradually increases for 5 minutes.
The heart rate decreases for 6 minutes, remains constant for 19 minutes, and then gradually increases for 5 minutes.
The heart rate increases for 6 minutes, remains constant for 19 minutes, and then gradually decreases for 5 minutes.
The heart rate remains constant for 6 minutes, increases for 19 minutes, and then gradually decreases for 5 minutes.