Question

which is a cardio workout that you can change to keep things interesting?
running
sitting down for a breather
weightlifting

Explanation:

A cardio workout is an exercise that increases heart rate and improves cardiovascular health. Running is a classic cardio exercise, and it can be varied (e.g., changing pace, distance, terrain) to keep it interesting. "Sitting down for a breather" is not a workout, and weightlifting is a strength - training exercise, not primarily cardio.

Answer:

A. Running