The ____________ of the printer is often believed to have been one of the most important of the last 500 years.

The answer "Invention" is the most fitting choice in this context because it specifically refers to the act of creating something new that has not existed before. The printer, as a technological advancement, is considered a groundbreaking invention that revolutionized the way information was disseminated and fundamentally changed communication and learning throughout history.

While "Development," "Creation," and "Innovation" may seem relevant, they each imply a slightly different concept. "Development" often suggests the process of improving or refining an existing idea rather than the initial conceptualization. "Creation" can refer to the act of bringing something into existence but does not carry the historical connotation of being a major breakthrough as "invention" does. "Innovation" indicates the improvement or application of an invention, which is also valuable but focuses more on modifications rather than the original concept itself. Therefore, "Invention" best captures the significance of the printer's impact.