Answer: a) The loss of slave labor in the south to work the fields
Step-by-step explanation:
"Cotton was the biggest crop in the south; if there weren't enough hands in the field to produce it, the southern economy would hit rock bottom."
The South didn't win the Civil War, so D is incorrect. Americans didn't move on to silk, so B is incorrect. Plantation owners didn't all die, there were still a considerable amount after the war, so C is incorrect.