Questions 21-25 are based on the following passage:

　　This book has been written for two types of students. One is the student who is learning English in order to study some other subjects. The other is the student who needs to learn how to write essays as a part of his university course.

　　As its title suggests, the book’s main aim is to teach writing. But each unit contains a passage of English, followed by exercises to make sure you have understood how that passage is organized. Why is so much reading practice given in a book? Simply because you wish to organize your own essays correctly, it is important to understand how other writers have organized their passages.

　　Each unit of this book is about a different subject. These subjects in this book have been chosen because of their general interest, and you do not have to be an expert on each subject to follow the units. Even so, the student who is learning English in order to study some other subjects may ask whether he would spend his time better reading and writing about his own subject. This is not necessary true. Essays, reports and articles have a lot in common, whether they are about chemistry or sociology. So the chemist and the sociologist can learn a lot about writing good English by reading and writing passages on subjects of general interest.

　　21. The book is mainly designed for __________.

　　A. middle school teachers B. professional writers

　　C. organizers and designers D. college students

　　22. The main reason for much reading in the book is that ________.

　　A. readers would like to read more then write more

　　B. readers need to do more reading practice for interest

　　C. readers need to know how the article is arranged

　　D. readers will have a better understanding of the reading

　　23. Every unit in this book is mainly composed of __________ sections.

　　A. two B. three C. five D. six

　　24. This book is useful for the students because it ____________.

　　A. talks about the reading skills B. discusses the writing skills only

　　C. contains interesting materials D. is about chemistry and sociology

　　25. It can be concluded that this book is a ___________.

　　A. reading textbook B. writing textbook

　　C. listening textbook D. translation textbook