Select the most appropriate option to fill in the blank.

Any resemblance of a character in this book to a living person is ______ incidental.

purely

The correct option to fill in the blank is purely incidental.

The phrase "purely incidental" means "not intended or planned; happening by chance". It is the most accurate word to describe the resemblance of a character in a book to a living person.

The other options are incorrect.

• Absolutely means "without doubt or qualification". It is not the correct word to use in this sentence because it is not possible to be absolutely sure that the resemblance is incidental.
• Naturally means "in a normal or expected way". It is not the correct word to use in this sentence because the resemblance is not something that would happen naturally.
• Thoroughly means "in a complete or careful way". It is not the correct word to use in this sentence because it is not necessary to be thorough in order to say that the resemblance is incidental.