Which of the following types of classified materials require standard classification markings?

The correct answer is based on the understanding of how various forms of communication are treated when it comes to classified information. Instant messages, which can include sensitive discussions or information transmitted in real-time, often have the potential to contain classified content that requires protective measures. Standard classification markings are vital for ensuring that recipients of such messages understand the sensitivity level of the information being shared, helping to maintain confidentiality and security protocols.

In contrast, text messages and social media posts typically fall under specific usage guidelines that might not necessitate formal classification markings, especially if they are casually used or within unsecured channels. Public announcements are generally intended for broader communication and transparency, which does not align with the requirement for classified materials to be marked due to the nature and intent behind their distribution. Therefore, standard classification markings are essential for instant messages to denote their classified status and ensure that their sensitive content is appropriately protected.