Written messages refer to any form of communication that is conveyed through written text. This can include letters, emails, memos, notes, and any other form of written communication. In the given options, the correct answer is option 'A', which includes letters and emails.

Explanation:

- Letters: Letters are one of the oldest forms of written communication. They are typically written on paper and sent through the postal system. Letters are used for various purposes, such as personal correspondence, business communication, and formal invitations.

- Emails: Emails are electronic messages that are sent and received via the internet. They have become a popular and convenient method of communication in both personal and professional settings. Emails can be used to send text messages, attachments, and even multimedia content.

- Television and radio: Television and radio are not considered written messages. They are forms of communication that rely on audio and visual elements rather than written text. Television broadcasts use moving images and sound to convey information and entertainment, while radio broadcasts use only sound.

- Telephone and television: Similar to the previous option, telephone and television are not written messages. The telephone is a device used for voice communication, allowing people to have real-time conversations. Television, as mentioned earlier, is a medium that relies on audio and visual elements.

- Radio and theater: Radio and theater are also not written messages. Radio broadcasts use sound to convey information and entertainment, while theater involves live performances with actors and sets. Both mediums rely on audio and visual elements rather than written text.

In conclusion, written messages refer to forms of communication that are conveyed through written text. Letters and emails are examples of written messages, while options such as television, radio, telephone, and theater are not considered written messages.