Explanation:

Here’s how these options stack up:

- Autonomous: means independent or self-governing. Think of a robot or a country making its own decisions. Doesn’t fit the idea of an unknown author.

- Anomalous: means unusual or out of the ordinary. Something that doesn’t fit the pattern. But again, that’s not about identity.

- Anonymous: this is your winner . Means something done by someone whose name is not known—like a poem or letter where nobody knows who wrote it. Exact match!

- Autocrat: is a ruler with absolute power. Not even close in meaning to having an unknown author.

So, we’re talking about a work whose creator is unknown—the one-word substitute is definitely Anonymous.