Final answer:
In 'Dead Poets Society,' Mr. Keating tells his students they may call him 'O Captain, My Captain,' which is option C.
Step-by-step explanation:
In the film Dead Poets Society, the character Mr. Keating, played by Robin Williams, tells his students that they may call him 'O Captain, My Captain', a reference to the poem by Walt Whitman. This term of endearment and respect originates from the poem's appreciation of a leader's guidance, mirroring Mr. Keating's influential role among his students in the film. The correct answer to what Mr. Keating tells his students they may call him is C) O Captain, My Captain.