Select the correct answer.

Mark is 18 years old and currently exercises for 1 hour a week with moderate-intensity aerobic exercise, and lifts weights three days a week. What changes could he make to his exercise routine to meet or exceed the physical activity guidelines?

A. Continue with his current exercise routine. Mark is currently meeting the physical activity guidelines.

B. Increase aerobic exercise to 20 hours a week with no rest days, and increase his weight lifting to 7 days a week.

C. Maintain his current exercise routine and add one hour of vigorous-intensity exercise.

D. Maintain his aerobic exercise routine, but decrease his weightlifting to two times a week.

E. Maintain his current aerobic exercise routine, but lift weights four days a week.