Which of the following items cannot be sent via Media Mail?

Media Mail is a special postal service designed for sending educational materials at a lower rate. It is specifically intended for items that have a legitimate educational purpose, such as books, printed music, and films, among others.

Advertising materials, however, are not eligible for Media Mail. This is because Media Mail is meant to facilitate the distribution of non-commercial items that serve an educational function rather than items intended for commercial promotion. Therefore, when sending materials that might promote a business or a specific product, those items must be sent using different mailing services that allow for advertising purposes.

The other options—books, films, and sound recordings—are all considered appropriate for Media Mail because they fit within the scope of educational or instructional content. Consequently, the identification of advertising materials as ineligible for Media Mail highlights the primary objective of this service, which is to support the distribution of educational and literary items.