The true statement about every public domain work is:
It is not protected by copyright or Creative Commons licenses.
Public domain works are free for anyone to use without permission, as they are no longer under copyright protection or do not fall under any Creative Commons licenses. The other statements may apply to many public domain works, but they are not universally true. For instance, not all public domain works are necessarily 100 years old, and they may not all be considered of great artistic or scientific merit.