Correct option is D
The correct answer is she could not explain the related concept effectively in the class.
The teacher should try to explain the major distinction between respiration and breathing that breathing is a physical process of exchange gases between cells and the environment. Respiration is the procedure by which energy is released from food in our body. The function of the respiratory system is to breathe in oxygen for respiration producing energy from food and to breathe out carbon dioxide produced by respiration.