The correct answer is A) a larger population.
An advantage for the North at the start of the Civil War was the North had a larger population.
The Civil War in the United States started by the many differences the Northern states had with the confederated states, basically on slavery. The North supported desegregation meanwhile the South supported slavery. Indeed, slavery was an important part of the Southern economy.
On April 12, 1861, the Confederated Army attacked Fort Sumter, in Charleston, South Carolina. This incident initiated the Civil War. One advantage for the North at the start of the Civil War was the North had a larger population.