Studies Conducted Among the Kipsigis of Western Kenya Demonstrate That

Studies conducted among the Kipsigis of Western Kenya demonstrate that

A) the Kipsigis' precocity in motor development is due to their genetic inheritance.
B) Kipsigis and American babies do not differ in the ages at which they achieve the motor milestones in the first year of life.
C) Kipsigis babies show advanced performance on motor skills for which they receive extensive practice, but not for those for which they don't.
D) American babies reach motor milestones at earlier ages than do Kipsigis babies, presumably because of better nutrition.