A flail chest occurs when:

A. more than three ribs are fractured on the same side of the chest.
B. a segment of fractured ribs bulges during the inhalation phase.
C. multiple ribs are fractured on both sides of the thoracic cage.
D. a segment of the chest wall is detached from the thoracic cage.

Answer: D. a segment of the chest wall is detached from the thoracic cage.