Terrible to say, but the creation of the cotton gin contributed to the growth of slavery, which already existed in the U.S since the 17th century. The answer is B.
The cotton gin did reduce labor for the removal of seeds, but growing cotton became more profitable after this invention was patented. Slave owners, especially those from the South (white, aristocratic land owners) wanted to make more profits, so the demand for slaves and land grew more after the invention of the cotton gin in 1792.