The correct option is A (C)→(B)→ (A)→(D)
The urge to breathe comes from the respiratory center, located at the base of brain. It sends signals via the spinal cord to diaphragm and the muscles between ribs telling them when to contract or relax. During inspiration, the diaphragm -- the large muscle that divides chest and abdomen -- contracts and moves downward. Additionally, ribs move outward. This enlarges your chest and lungs expand. Lung expansion creates a vacuum. Air enters the nose and mouth and is pulled into windpipe -- the trachea. The trachea divides into smaller airways called bronchi. These continue to divide as they get farther from the trachea, like the branches of a tree. Finally, the tiny airways deliver the air to the smallest structures in your lung -- the alveoli -- where gas exchange takes place.