Final answer:
Priam suspects Hermes' true identity when he notices Hermes' divine aura, which is option (b). This type of recognition is a frequent motif in Greek literature, where characters reveal or deduce the truth through different means.
Step-by-step explanation:
In the narrative involving Priam and Hermes, it can be inferred that Priam suspects Hermes is more than he appears when he recognizes the god-like characteristics despite Hermes' disguise as a mortal. The correct option that reflects how Priam suspects Hermes' true identity is Priam notices Hermes' divine aura and recognizes him, which translates to option (b) in the multiple-choice answers. This is a common theme in Greek mythology, where gods often disguise themselves, but certain characters can perceive the truth either through divine aura, reasoning, or other signs.
This form of recognition or anagnorisis is frequent in classical literature, where characters discern a deeper truth through various means, whether it's the use of reason, as seen in 'the Choephori' or the perception of a god's radiance despite their mortal guise, as possibly intuited by Priam.