Final answer:
A hornbook was an educational tool consisting of a wooden paddle with a single paper sheet pasted on it, typically covered with a thin horn sheet, hence it contained just one page. Option C is correct.
Step-by-step explanation:
A hornbook was a tool used for educational purposes, particularly during the Tudor and early colonial periods. It was not a book in the traditional sense but rather a single wooden paddle with a handle, where a sheet of paper was pasted that contained the alphabet, and sometimes syllables or religious verses, protected by a thin sheet of transparent horn. Therefore, the correct answer to how big was a hornbook is C. 1 page.