Why Must Chest Tubes Be Attached to a Water-Seal Drainage

Multiple Choice

Why must chest tubes be attached to a water-seal drainage system?

A) to keep the pleural cavity humid
B) to add weight to the drainage device to keep it upright
C) to keep the microbial count in the drainage from reentering
D) to keep air from reentering thoracic space to reestablish negative pressure for respiration