Hello, I'm sorry to hear that you were disappointed with the textbook. I would like to leave an explanation about this textbook for future buyers to reference. 1. The content of the e-book contains material equivalent to one computer science major course. Therefore, the content is broadly spread out at a 'liberal arts course' level. All content in this textbook is based on past exam questions and official materials from testing organizations, and was created by selecting content that could most likely appear on exams through past exam questions. 2. The e-book textbook was designed to help you achieve around 70-80 points when studied three times. Since the content of each of the 5 subjects is extensive and many questions are closely related to practical work, it would be difficult to cover all content even if you memorize the official textbook or this entire textbook. 3. This textbook was created for those who find it difficult to study the official textbook (5 volumes + 1300 pages), allowing them to challenge the certification with less burden. For those who have time, I think it would be good to purchase the official textbook or study it alongside this textbook. As introduced in the course introduction video, purchasing only the 5th subject textbook, which has the most questions, is also one method. If you leave feedback about parts that were missing or disappointing in the textbook, I will try to reflect them more. Thank you.