Which one of the following is a type of book?

Both the "General textbook" and the "Reference book" are types of books.

Key Points

• A General Textbook is a standard book of study, which provides comprehensive coverage of topics in a particular subject area. General textbooks are often used in academic settings and are usually written in a manner that is easy to understand for students at different levels of education.
• A Reference Book is a type of book that provides facts and information on a particular subject area and is usually intended to be consulted for information on specific matters rather than read from beginning to end. Examples of reference books include dictionaries, encyclopedias, almanacs, atlases, etc.

Hence, we can conclude that both of the 1 and 2 options are correct.