Which of the following statements is true?
a. You should exercise for at least 20 minutes, five times a week to maintain cardiorespiratory endurance.
b. In order to develop muscular endurance, you should include three 30-minute sessions of anaerobic exercise each week.
c. Daily stretching exercises should include a bouncing motion.
d. As long as you include a 5- to 10-minute warm-up in your exercise routine, you don't have to include cooldown exercises as well.