The correct options are
C The breathing rate is the number of breaths in one minute.
D Normal breathing rate of an adult human is 15-18 times a minute.
∙ The percentage of carbon dioxide in exhaled air is 4.4% and in inhaled air is 0.04% (as present in the atmosphere).
∙ The percentage of oxygen in the inhaled air is the percentage of oxygen present in the atmosphere i.e., 21%. The percentage of oxygen in the exhaled air is 16.4%.
∙ The number of times a person breathes is termed as breathing rate. It is 15-18 times/min of an adult in resting state. During excercise it increases to 25 times/min.