Answer:
using what they already know.
Explanation:
When a reader makes a prediction when reading a story, he is already using what he knows from the book.
For example, Mary is reading a detective novel that centers around trying to catch a serial killer, she can make her predictions from what she already knows in the book.
Perhaps, so far there exists a character that fits the role of the serial killer, Mary can proceed to predict that at the end, that character will be unmasked as the serial killer.
