Which statement best describes the relationship between heart rate and time during exercise?
A
The heart rate increases for 6 minutes, remains constant for 18 minutes, and then gradually decreases for 6 minutes.B
The heart rate increases for 6 minutes, remains constant for 18 minutes, and then gradually increases for 6 minutes.C
The heart rate decreases for 6 minutes, remains constant for 18 minutes, and then gradually increases for 6 minutes.D
The heart rate remains constant for 6 minutes, increases for 18 minutes, and then gradually decreases for 6 minutes.