Airlines That Restrict the Use of Frequent Flyer Miles During

Airlines that restrict the use of frequent flyer miles during holiday periods likely do so because:

A) the opportunity cost to airlines of filling seats with frequent flyers is lower at these times.
B) the opportunity cost to airlines of filling seats with frequent flyers is higher at these times.
C) passengers have more transportation alternatives available to them at these times.
D) airlines want to protect their most loyal customers from the discomfort of overcrowded airplanes.