Answer:
C. When cardiorespiratory exercise is completed.
Step-by-step explanation:
Stretching is always a good idea, and there is not necessarily a set time for you to do so. However, stretching is more effective once cardiorespiratory exercise has been completed. This is because during exercise, you have been moving your muscles, and these will be warm. Moreover, you are likely to be more flexible because you have increased circulation to these muscles.