Shelly's Parents Are Worried Because Their Daughter Is 5 Months

Shelly's parents are worried because their daughter is 5 months old and can sit but not on her own.A psychologist friend tells them that:

A) this is normal,because most children cannot sit on their own until around 6 or 7 months.
B) they should take their daughter to the hospital because she may have neurological damage.
C) they should not worry because their daughter is actually a little bit ahead of schedule.
D) there is no set timeline for this to occur;it will just happen naturally whenever it happens.