Trey's family has been walking together for 20 minutes at least three days per week for the past four weeks. They already have so much more energy, and they want to continue to improve. How could Trey's family apply the FITT principles to make their walking routine more effective?
A. Add push-ups to their routine
B. Replace one walk with a bike ride
C. Add an extra day of walking each week
D. Wear new shoes to walk faster