It is called relevant.
Relevant is just a synonym to related, so if it's not related to the subject than it would be irrelevant.
Answer:
A letter was written to her father by Mona.
If i understood your question correctly a few good fantasy books include it can range from twighlight to harry potter to the hobbit to one of those sexy kind of books .some of my favorite are the hobbit;desimation of smaug or agent alex .
Answer:
An opinion that is different from a traditional belief