Answer:
A. increase the duration of his walking each day
Step-by-step explanation:
From the options that the question has:
A. Increase the duration of his walking each day
B. Add swimming to his current fitness routine
C. Carry a heavy backpack while walking
D. Alternate between a treadmill and walking outside
The one that best suits the idea of pregression to his routine is the one that states that increasein the duration of his walking everyday will help him achieve his goals of eventually being okay with marchin band practices for three to four hours.