In Wayne Dennis's study of infants in Iranian orphanages, only 15 percent of the orphans were walking alone by 3 to 4 years of age because

A) they spent the first year of their lives being carried by caregivers.
B) they were malnourished and unable to acquire the strength to walk.
C) they spent their days lying on their backs in cribs.
D) rapid motor progress was actively discouraged by caregivers.

Answer: C