During inhalation, which of the following occurs?

• A. The diaphragm contracts downward
• B. The diaphragm relaxes upward
• C. Intercostal muscles relax inward
• D. Pressure increases in lungs

Answer: (A)

The process being tested is how inhalation occurs: the diaphragm contracts and moves downward, enlarging the thoracic cavity. This increase in volume reduces the pressure inside the lungs below atmospheric pressure, causing air to flow in. The other statements don’t fit: the diaphragm relaxing upward would reduce thoracic volume and push air out, not in; intercostal muscles relax inward (instead of contracting to lift the rib cage) would not expand the chest; and pressure in the lungs actually decreases, not increases, during inhalation to draw air in.