One of the Key Developments Enabling the Union to Stop

Multiple Choice

One of the key developments enabling the Union to stop the Confederate thrust into the North at Antietam was

A) General Lee's dilly-dallying and half-hearted offensive thrust at Antietam Creek.
B) the Union's discovery of General Robert E. Lee's battle plans.
C) Lincoln's removal of General McClellan from his command.
D) the use of the new repeating rifle for the first time.
E) the death of Stonewall Jackson during the battle.