What is the main difference between cardio and strength-training activities?

A. Cardio activities increase your physical strength, while strength-training activities work your heart and lungs.
B. Cardio activities work your heart and lungs, while strength-training activities strengthen your muscles.
C. Cardio activities require short bursts of energy, while strength-training activities strengthen your body over long durations.
D. Cardio activities improve your joints' range of motion, while strength-training activities work your heart and lungs.