Which among the following statement is correct?
A. Normal breathing rate of a person is 15 to 18 times per minute.
B. Total area of gas exchange seen in the whole alveoli in two lungs is 36 to 72 square metre.
C. The total volume of air breathed in an out in the cycle of inhalation and exhalation is 500 ml.
D. Wind pipe is supported by rings of cartilage in order to avoid its collapse when there is lesser air in it.