Which of the Following Are Goals of Airway Clearance Therapy

Which of the following are goals of airway clearance therapy?
1) Help reverse the underlying disease process.
2) Help mobilize retained secretion.
3) Improve pulmonary gas exchange.
4) Reduce the work of breathing.

A) 1 and 3 only
B) 1, 2, and 3 only
C) 3 and 4 only
D) 2, 3, and 4 only