What Is the Primary Barrier That Prevents Chimpanzees from Learning

What is the primary barrier that prevents chimpanzees from learning to speak?

A) Their mouths and throats are not equipped to produce spoken words the way we do.
B) Their main form of communication is gestural, rather than vocal.
C) They cannot focus their attention on a complex cognitive task like word-learning.
D) They cannot grasp the symbolic aspects of human language.