The correct answer to this open question is the following.
The question does not include options. However, we can say the following.
The southern invention that was created to combat the union naval blockade was precisely the blockade runner.
Let's have in mind that the Union Army had decided to naval blockade all the cotton trade from the Confederate states, trying to stop the southern economy and made them suffer from the lack of provisions. That is why southerners had to invent the blockade runner, a kind of vessel that could avoid the blockades. These small ships were fast, so instead of confronting larger union ships, blockade runners just needed to be faster and get lost to the Union vessels.
