Which of the following would be the best material to use to research the historical references made in wheatley's "to his excellency, general washington"? atlas, dictionary, encyclopedia, or thesaurus?

I think the correct answer from  the choices listed above is the third option. It would be the encyclopedia  the best material to use to research the historical references made in wheatley's "to his excellency, general washington". It is a book or set of books giving information on many subjects or on many aspects of one subject and typically arranged alphabetically.