The correct answer is A. Throguh letters written home
Step-by-step explanation:
The Civil War was a conflict that occurred in the U.S. from 1861 to 1865 as a result of differences between the Northern and the Southern states. Considering this war occurred a long time ago there are few sources of information that provide information about "firsthand experiences" or the experiences of people who participated in the war as they are not anymore alive, the main source and way to learn about their experiences during the civil war has been through the letters soldiers wrote to their families, friends, etc during the war as in them soldiers describe the events that occurred and also their perceptions and point of view as they experienced the war. Therefore, the main way we have learned about soldiers firsthand experiences during the civil war is through letters written home.