Final answer:
The example of imagery in Walt Whitman's O Captain! My Captain! is the description of the sound of the bells. Therefore, the correct option is D. The description of the sound of the bells.
Step-by-step explanation:
The example of imagery in Walt Whitman's O Captain! My Captain! is D. The description of the sound of the bells. In the poem, Whitman describes the sound of bells as a representation of the joy and celebration that accompanies the ship's return. This description appeals to the reader's sense of hearing, creating a vivid image of the scene.