Kevin burns 5.5 cal/min by walking at a speed of 4.5 miles per hour. He is also able to have a conversation while performing this moderately intense physical activity. What effect does this activity have on his breathing and heart rate:

A. a slight change in his breathing but no change in his heart rate
B. no change in his breathing but a significant change in his heart rate
C. a significant change in both his breathing and heart rate
D. a slight increase in both his breathing and heart rate e. little to no change in his breathing and heart rate