Hello there! The Cumberland Gap was a route to get past the Cumberland Mountains in the Appalachian Range and head to the west. It was not an area to grow cops, because you can't grow crops well in mountainous areas and it wasn't exactly a place for colonists to settle either. Therefore, A and B are out. It doesn't really have to do much with river travel. That answer doesn't make too much sense either. As explained before, it was just a mountain passage to get through and head farther west. The answer is D.