Rearrange the sentences (A), (B), (C), (D), (E) and (F) in a proper sequence so as to form a meaningful paragraph and then answer the given questions.
(A) But it is normal for rates to vary somewhat.
(B) The rate at which these actions emerge is sometimes a worry for parents.
(C) As a child grows, his or her nervous system becomes more mature.
(D) Having said that variation is normal, nearly all children begin to exhibit certain motor skills at a fairly consistent rate unless some type of disability is present.
(E) As this happens, the child becomes more and more capable of performing increasingly complex actions.
(F) Hence, they frequently fret about whether or not their children are developing these skills at a normal rate.
Which of the following should be the THIRD sentence after the rearrangement?