Kipsigi Infants Walk Considerably Earlier Than North American Infants Because

Kipsigi infants walk considerably earlier than North American infants because

A) Kipsigi babies are smaller at birth, requiring less leg-muscle strength for standing.
B) Kipsigi babies have a genetic tendency toward early motor development.
C) North American babies are mentally overstimulated, resulting in less motivation to walk.
D) Kipsigi parents emphasize early motor maturity, practicing formal exercises to stimulate particular skills.