Which is most likely the length of a student’s textbook?

A textbook is usually a few dozen centimeters long. Thirty centimeters is a reasonable length: it is about the length of a large ruler. Thirty millimeters is only 3 centimeters, while 30 decimeters is 3 meters and 30 hectometers is 3,000 meters, all unreasonable for a textbook.

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