The best cardio respiratory workout is one that A. Produces a high amount of sweat.
B. Makes you extremely tired.
C. Makes you extremely sore the next day.
D. You’ll perform on a regular basis.

D. You’ll perform on a regular basis.

Explanation:

The best cardiorespiratory workout is one that you will perform on a regular basis - c. This indeed probably is something that's very important because without regular workouts, no exercise will help you as one that you're doing on a regular basis.