After the defeat at the First Battle of Bull Run, the Union army around Washington, D. C., spent time rebuilding and training. The army began to be known as the Army of the Potomac, after a river in the area. Imagine that you are a historian interested in the daily routine of ordinary soldiers in the Army of the Potomac. Below are some primary sources, or sources made during the time period being studied. Which source would be most useful to you?

A. a newspaper article about the commander of the army
B. a letter written by a new recruit to the army
C. a speech given by a congressman visiting the army
D. a memoir written by a former Confederate prisoner