What unusual event does the guard recount occurring just before Antigone returned to the body?

The correct answer highlights a dust storm as the unusual event that the guard recounts. This detail is significant as it sets the scene for Antigone's actions and emphasizes an atmosphere of turmoil and chaos. The dust storm symbolizes the tumultuous emotions and conflicts surrounding the burial of Polynices, reflecting the underlying themes of disorder and fate in the play.

The other options, such as a lightning strike, heavy snowfall, or a loud thunderclap, do not capture the specific environmental context that the dust storm represents in relation to the narrative. The choice of a dust storm adds a layer of dramatic effect, enhancing the tension and foreboding surrounding Antigone's bold decision to defy Creon and honor her brother with a proper burial. This moment encapsulates the struggle between individual moral duty and state law, which is a central theme of Sophocles' work.