Correct Answer: They are assigned to work as laborers in a factory at another camp, Buna. (SOURCE) I took the test, and got this answer correct. I hope you have fun in your readings.
Whitman had written a long poem and some of the readers might feel bored reading it, so he used this device to give some energy to it. Since anaphora is repetition, it keeps on getting in the mind of the readers thus giving emphasis to the ideas he expresses.