Part A
The correct answer is B. to persuade the nation to support the movement toward racial justice. President Kennedy's speech emphasizes the moral crisis the nation faces regarding civil rights and calls for action to make changes in a peaceful and constructive manner.
Part B
The sentence that best supports the answer to Part A is D. A great change is at hand, and our task, our obligation, is to make that revolution, that change, peaceful and constructive for all. (paragraph 4) This sentence highlights the need for collective action toward racial justice, reinforcing the persuasive nature of his message.