Andy and Jeff Compare the Physical Development of Their Sons

Andy and Jeff compare the physical development of their sons. The baby boys are the same age. Andy brags that his infant son seems to be maturing at an advanced rate compared to what Jeff is observing in his son. Jeff worries that maybe there is something physically wrong with his son. Jeff consults a developmental book and finds that:

A) not all children achieve the same physical skills in the same order
B) all children achieve the same physical skills, just at varying times
C) the sequence of acquiring physical skills varies between individuals
D) the sequence of acquiring physical skills varies between cultures