Which of the following is a common element of military ceremonies?

Military ceremonies typically include the presence of musical units as a common element. This aspect adds a formal, celebratory atmosphere to events such as change of command ceremonies, retirement observances, and memorial services. The music can range from traditional military marches to patriotic songs, helping to evoke a sense of pride and honor, which is essential in reinforcing the significance of the ceremony.

Other elements listed, like casual attire, public announcements, and open invitations, do not align with the formal and structured nature of military ceremonies. Attire at such events is generally formal, reflecting the discipline and traditions of the military, while public announcements are not a standard feature of every ceremony. Invitations tend to be targeted to specific attendees rather than open to the general public, further highlighting the exclusive and formal context of these events.