Final answer:
An example of a strength-training activity is sit-ups. Tennis, hopscotch, and jump roping are not strength-training activities.
Step-by-step explanation:
An example of a strength-training activity is sit-ups. Strength training involves using resistance to build muscle strength and endurance. Sit-ups specifically target the abdominal muscles, helping to improve core strength and stability.
On the other hand, tennis, hopscotch, and jump roping are more focused on cardiovascular fitness and agility.
Learn more about strength-training activities