Final answer:
It is true that, in controlled conditions, chimpanzees and gorillas can learn American Sign Language and exhibit language traits such as displacement and productivity, similar to human language, as exemplified by the gorilla Koko who learned over a thousand signs.
Step-by-step explanation:
Chimpanzees and gorillas have been subjects of research to determine if they can learn and use American Sign Language. Studies have shown that these great apes are capable of learning a basic vocabulary and utilizing simple words and word combinations. An example of such capability is Koko, a gorilla taught by Dr. Francine Patterson, who learned over a thousand signs and exhibited the ability to comment on things not immediately present, showcasing both displacement and productivity in language use, thus the statement is true.
Therefore, it is true that in controlled conditions, chimpanzees and gorillas can learn American Sign Language and use this language to exhibit both displacement and productivity. However, it is worth noting that many linguists remain skeptical and debate continues about the extent to which these abilities are comparable to human language.