Read this excerpt from a book about machines. This book is divided into six parts. Each has information about one of the six types of machines: the wheel and axle (it changed civilization!); the inclined plane (those ramps!); the wedge; the lever; the pulley; and the screw (yes, it’s a simple machine). Each part includes some simple examples along with some of the complex structures that I have designed using one or more of these simple machines.

What text feature might include this passage?

references
introduction
acknowledgements
advantages and disadvantages