Kipsigi Babies in Kenya, Who Are Given Training by Parents

Kipsigi babies in Kenya, who are given training by parents in sitting, standing, and walking:

A) reach these milestones at later ages than American children do.
B) are advanced in these skills, and also in other motor skills which have not been taught.
C) reach these motor milestones at the same ages as American children who have not received training.
D) develop these skills earlier than American children but are not advanced in motor skills which have not been taught.