In Mechanically Ventilated Patients, the Addition of Positive End-Expiratory Pressure

In mechanically ventilated patients, the addition of positive end-expiratory pressure (PEEP) to normal tidal volumes is associated with which of the following effects?
1) Decrease in intrapulmonary shunting
2) Increase in functional residual capacity
3) Increase in partial pressure of arterial oxygen (PaO₂)
4) Increase in residual volume

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