True. Ventilation perfusion coupling is the relationship between the amount of air reaching the air sacs of the lungs and the amount of blood reaching the lungs (mechanisms which maintain the correct proportion between alveolar airflow and pulmonary capillary blood flow). The amount of oxygen that reaches the alveoli is the ventilation. The amount of blood that gets to the alveoli is the perfusion. Alveolar ventilation brings oxygen into the lung and removes carbon dioxide. The mixed venous blood brings carbon dioxide into the lung and takes up alveolar oxygen.
The answer is; Physical weathering by water would carve out the face of the cliff.
The bottom of the cliff would register the greatest weathering because of the force of the water hitting the rocks in the fall. As a cave is curved from the base of the cliff, the overhanging part of the cliff eventually collapses hence retracting the cliff a small distance upstream of the river. The diagram below demonstrates this;
