What Contribution Do Studies of Deaf Children Born to Hearing

What contribution do studies of deaf children born to hearing parents make to our understanding of the language acquisition process?

A) They prove that it is sufficient to be raised in an environment where the actions of all other participants are organized by human language and culture.
B) If the parents do not use sign language, deaf children will not use more than a single sign in any "utterance."
C) They point to the importance of active participation of the child in language-mediated activity.
D) Hearing is essential to acquire language.