Final answer:
The phrase is an example of repetition, a rhetorical device that emphasizes an idea by stating it multiple times and enhances memorability and power of the speaker's message. Option number b is correct.
Step-by-step explanation:
The phrase "I have a dream today. I have a dream today." is an example of repetition. Repetition is a rhetorical device used to emphasize an idea or a concept by stating it multiple times. It is not an analogy, a rhetorical question, or specifically parallel structure, though it may contribute to parallelism in a broader context. The speaker, Martin Luther King Jr. in his famous speech, uses repetition to reinforce his vision and make the message more memorable and powerful.
Anaphora is a form of repetition where the same word or group of words is used at the beginning of successive sentences or clauses. In the speech, King effectively employs anaphora to evoke emotion and encourage the listeners to visualize the dream he is describing.