Final answer:
The sentence that requires a citation in a research project is the one about the increase in racial disparity in the U.S. prison population over the last decade as it claims a specific documented change.
Step-by-step explanation:
In a research project, the sentence that would need a citation is: "The racial disparity in the prison population of the United States has increased in the last 10 years." This statement presents specific information that implies a documented change over a period of time and would therefore require evidential support from a credible source to back up the claim.
On the other hand, sentences like "Thanksgiving is celebrated on the third Thursday of November in the United States," "The first enslaved people were brought to the United States in 1619," and "Phyllis Wheatley was born on or around 1753 and died in 1784" represent commonly known historical facts or specific dates that are widely recognized and could be considered common knowledge, generally not requiring citation in a research project.