Answer:
D. The slave's bias: Though the servant does not think highly of the president, the first-hand account serves as an excellent resource in understanding the president's treatment and management of a minority, namely his African American slaves.
Step-by-step explanation:
When deciding to use the described source, the challenge that a researcher should consider is the slave's bias. When we're writing a research paper, we should do our best to use objective sources - sources based on facts and uninfluenced by the writer's feelings, opinions, beliefs, and assumptions.
However, Marlena is writing a paper on President Andrew Jackson's treatment of minorities. The information those minorities left about the treatment they endured is important. Using a biased source is alright and maybe even necessary in this case.