Both Continuous Positive Airway Pressure (CPAP)and Bilevel Positive Airway Pressure

Both continuous positive airway pressure (CPAP) and Bilevel positive airway pressure (BiPAP) modes of airway provide positive airway pressure to keep airways open.What is the main difference between these two modes?

A) CPAP maintains a positive airway pressure measured in millimeters of mercury (mm Hg)
B) CPAP uses two modes of pressure during inspiration and expiration
C) BiPAP uses two modes of pressure during inspiration and expiration
D) BiPAP does not deliver enough expiratory pressure to keep airways open