“No one knows when chimps and humans first came into contact, but it seems certain that Africans have long interacted with chimps.” Which words tell the reader that this sentence contains subjective language?

“No one knows when chimps and humans first came into contact, but it seems certain  that Africans have long interacted with chimps.”

Explanation:

the statement that best explains why the tenth amendment reserves some rights and powers to states is that the framers believed in the principle of federalism. this principle says that some powers are in the hands of a centralized national government, while others are reserved for the governments of several states.

yes, no, maybe, so i honestly don't know best of luck