The correct option is
A Thorax
The thoracic cavity is an airtight chamber which lodges the lungs. It is guarded dorsally by the vertebral column, ventrally be sternum, laterally by ribs and on the lower side by the diaphragm.
Thoracic chamber should be airtight in order to maintain different air volumes in the lungs at different phases of respiration. Any change in the thoracic volume will be reflected in the pulmonary volume.
So the correct option is "Thoracic".