Head Turning to Sounds Occurs at Birth, Disappears a Month

Head turning to sounds occurs at birth, disappears a month later, only to reappear at 3 or 4 months of age. This exemplifies

A) a U-shaped function.
B) a post-neonatal function.
C) that 4 month olds have had functional neck muscles since birth.
D) that this response to sound at birth is reflexive and not a true indication of hearing ability, as it is at 3 or 4 months of age.