After Congress banned the importation of slaves,

a. the slave population decreased dramatically.

b. most southern states voted to end slavery.

c. the slave population increased dramatically.

d. the cotton industry collapsed.

To answer this question, we need to understand the historical context. The ban on the importation of slaves was enacted by the United States Congress in 1808 through the passage of the Act Prohibiting Importation of Slaves. This law made it illegal to import slaves from Africa or any foreign country into the United States.

After the ban on slave importation, the correct answer to your question is:

a. the slave population decreased dramatically.

Explanation: The ban on importing slaves meant that no new slaves could be legally brought into the country. This resulted in a decrease in the slave population over time because slaves were no longer being imported to replace those who died or were freed. As a result, the existing slave population was not replenished, leading to a decline in numbers.

It is important to note that while the ban on the importation of slaves did contribute to a decrease in the slave population, it did not lead to the immediate end of slavery or widespread emancipation. Slavery continued to be legal in the southern states, and the practice persisted for several more decades until the abolition movement gained momentum.