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.