(B) lifted ribs and flattened diaphragm.
When a person breathes in (inhalation), the ribs are lifted upward and outward by intercostal muscles, and the diaphragm contracts and flattens, increasing chest cavity volume and allowing air to rush in.
During inhalation, both the ribs moving up/out AND the diaphragm flattening work together to increase the volume of the thoracic cavity, reducing air pressure inside so air flows in. Option (A) is wrong because dome-shaped diaphragm occurs during exhalation. Options (C) and (D) describe exhalation. The key is: inhalation = ribs lifted + diaphragm flattened.