Which Statement About Birds Is Most Accurate

Which statement about birds is most accurate?

A) Birds are primarily a species that is preyed on and tend to mask signs of illness as a means of self-preservation.
B) Birds are very sensitive to changes in their environment, diet, and routine, so changes in their behavior, attitude, or physical condition usually are temporary and of no great concern.
C) The bird's gender can usually be determined by its size and coloration, and by gently parting the vent to look for a penis.
D) Leg bands should never be removed from domestic birds because they are essential for proper identification.