What is a requirement for magazines and newspapers to be categorized as periodicals?

For materials to be categorized as periodicals, they must generally be published at regular intervals. This regularity is a defining characteristic of periodicals, distinguishing them from single publications or one-time issues. Magazines and newspapers can be classified as periodicals if they are published regularly, which can include a range of frequencies such as daily, weekly, monthly, or quarterly.

Option C, which states that periodicals must be printed monthly, aligns with this understanding since monthly publications maintain a consistent schedule that defines them as periodicals. However, it is important to note that periodicals do not require a specific frequency of monthly publication; they can also be published weekly or even daily. In this context, the monthly frequency is an acceptable standard that fulfills the requirement for categorization as a periodical, allowing for regular dissemination of content to readers.

The other options suggest specific frequencies that, while valid forms of publication, are more restrictive and do not encompass the broader definition of what can be considered a periodical. Therefore, the correct choice captures a widely recognized periodical schedule that fits the criteria for various types of regular publications.