If a child starts to speak later than others, he will in future

A．he owes his speech ability to good nursing
B．he has a brain more complex than an animal's
C．he can produce his own sentences
D．he is born with the capacity to speak

A．find out what role careful nursing would play in teaching child to speak
B．discover what language a child would speak without hearing any human speech
C．prove that children are born with the ability to speak
D．prove that a child be damaged without learning a language