For example, academic textbooks. The book that is used to communicate Government or in the business and get the substance often is a person in the same band, or a band of the same profession in the field of business.
The books used as textbooks consecutive government or the business community receivers and senders are often the same people in the same profession or the same in business.
Such as the academic books used for official or business circles ผู้ส่งสาร receiver and is often a person in the same or the same profession for the business.