The correct answer is D, the repetition intensifies the speaker's sense of urgency.
The use of the word "must" in this excerpt does not show any sign of anger. Anger could be expressed by the use of exclamation marks, for example, or adjectives, but not by the use of "must". Therefore, it also doesn't suggest that the speaker is intimidating or demanding.
The use of repetition is what gives us the sense of urgency. By being followed by different sentences, always using the word "must", we feel that this is important and we need to hurry up and do it.
