Depending on the license you are looking to obtain, it will determine the books you need. Each license will have specifics books meant for their exams. The State and County have a document called the Exam Reference List, which shows the list of books and their editions. The books which will be brought into testing can contain underlining with a pen, have permanent tabs, or have highlighting.
The books are apart of the requirement an individual will need to have for testing. The references will allow you to study and find answers during the exam.