Answer: B. parallelism
Parallelism is a rhetorical device that repeats the same words or words with similar meanings in a certain pattern. This makes the text balanced and provides a particular rhythm to the speech, which can make it more persuasive. It is one of the most basic principles of rhetoric. In this case, by repeating the phrase "I don't believe" twice, Dr. King is increasing the rhythm and persuasiveness of his speech.