In the context of the question, the correct answer is:
B. morphine
Explanation:
1. During the Civil War, morphine was commonly used as a pain reliever for wounded soldiers.
2. Due to its widespread use, many veterans became addicted to morphine, leading to a significant issue of addiction among Civil War veterans.
3. This addiction to morphine among Civil War veterans is a historical fact that reflects the medical practices and challenges of that time period.
Therefore, the correct choice in this question is B. morphine, as it accurately reflects the historical context of Civil War veterans and their struggle with addiction to this pain-relieving medication.
