A middle school physical education teacher wants to incorporate submaximal intensity activities, such as walking and jogging for developing cardiorespiratory fitness. In order to complete an effective aerobic workout, the students should engage in aerobic activities at an intensity of 60% to 90% of maximum oxygen uptake for 3-5 days a week. What minimum number of minutes per session of continued or interval activity is required to achieve cardiorespiratory fitness?
A. 15-minute exercise session
B. 20-minute exercise session
C. 30-minute exercise session
D. 45-minute exercise session
