Final answer:
Without specific information about the play and characters' interactions in Act I, it is not possible to accurately determine the antagonists from the names provided.
Step-by-step explanation:
The characters listed do not appear to be connected to a single play or script, and given the provided context does not match the characters, it is not possible to determine which characters among Annie, Kate Keller, James, Captain Keller, and Helen are antagonists without specific information about the actions taking place in the given part of Act I. In script analysis, often referred to by Aristotle and his elements, an antagonist is a character who opposes the protagonist and creates conflict within the narrative.
However, without further information about the script and the characters' roles and relationships, selecting antagonists is not feasible. Terms such as blocking and blocking positions, arena stage, and black box are relevant in the theatre context, referring to the movements and stage type, but do not aid in identifying antagonists without additional details.