The correct answer is B) They were worried that the government would put restrictions on the slave trade.
During the end of the 1700's, the Southern states were extremely reliant on the production of cash crops (like tobacco, rice, and cotton). To create these crops, some Southerners relied on slave labor.
With this in mind, Southerners feared that the federal government's ability to regulate interstate commerece would result in the banning of the slave trade. If the slave trade was banned, than this would greatly decrease the slave population in the US, cutting into the profits of wealthy plantation owners.