Final answer:
During inhalation, the diaphragm contracts and the lungs expand, allowing air to flow in.
Step-by-step explanation:
During inhalation, the diaphragm contracts and moves downward, while the chest expands. This creates more space in the thoracic cavity, allowing the lungs to expand. As a result, air flows into the lungs. Therefore, the correct answer is option A) Diaphragm contracts, lungs expand.