Your teacher assigns you a research paper on political changes in the united states during the civil war. which source would best aid your research?

If you have these choices; Your answer is A book containing the letters of a US senator during the war.

A) a textbook chapter discussing Abraham Lincoln’s presidency.
B) an atlas showing famous battles and events during the war.
C) a book containing the letters of a US senator during the war.
D) a phone interview with a famous Civil War political historian