Which of these protects something someone has created, such as a piece of writing?

The correct answer is C. A copyright.

A copyright is a legal protection granted to the creators of original works, such as writings, music, and art. It gives the creator exclusive rights to use, distribute, and reproduce their work, preventing others from using it without permission. Paraphrasing, credible sources, and public domain refer to different concepts that do not provide the same type of legal protection.

If you have more questions or need further assistance, feel free to ask!