Which of the following is considered a type of direct mail?

The correct answer is personalized letters because they are a form of direct mail that is specifically designed to reach individual recipients directly through postal services. Direct mail involves sending promotional materials directly to potential customers' addresses, and personalized letters exemplify this method as they can be tailored to the recipient, thereby enhancing engagement and response rates. This personal touch often makes direct mail campaigns more effective, as they can address the recipient by name and include relevant content that speaks to their interests.

In contrast, television commercials, billboards, and online banners represent forms of advertising that are primarily non-direct, as they reach a broader audience. Television commercials broadcast to viewers in general, billboards display messages to anyone passing by, and online banners are placed on websites where visitors can see them without targeting individuals specifically. These forms of communication lack the personalized approach that is characteristic of direct mail, which is focused on creating a connection with the recipient.