Answer:
D. Soldiers on horseback: Calvary Units in the Trans-Mississippi region
Step-by-step explanation:
A. Fighting for freedom: African American Bridges
The book narrates the story of African American soldiers fighting for the Union.
B. In enemy territory: Battles fought in the north
Did not find anything abouth this.
C. Under siege: Civil War cities under attack
Attacks on Texas cities were not a big part of the Civil War.
D. Soldiers on horseback: Calvary Units in the Trans-Mississippi region
Texas biggest utility in the Civil War was supplying soldiers, so this is the correct answer.