Sign Language Acquisition in Primates Has Been Criticized on the Basis

Sign language acquisition in primates has been criticized on the basis that __________.

A) the signs were just imitative, were often random combinations, and did not involve a two-way conversation
B) chimpanzees and gorillas are not smart enough to learn sign language
C) chimpanzee and gorilla hands are not really capable of making most signs in ASL
D) primates already have a communication system, so they cannot learn another one