Which of the following describes Cameron's communication abilities? Group of answer choices:
a) He was selectively mute, talking only to his mother and brother but not to any school personnel
b) He asked and answered questions in complete sentences, and carried on conversations
c) He was non-vocal and communicated using picture exchange and approximations of sign language
d) He answered questions using one-or-two word phrases, and his expressive vocabulary was consistent with someone 2-3 years younger than his chronological age