The answer is D. The crash led to unemployment for millions of workers.
A.
After the Civil War Abraham Lincoln was just the first of many US Presidents to encourage immigration through economic and politic measures (one of them was to give free land to anyone willing to work it). The country needed people to rebuild itself and to settle the west of the continent. And everyone was aware that there is plenty of space.
Eli Whitney was the one with the cotton
James Watt was the one with the coal and water
And Jethro Tull Was the reduced number of workers to plant crops.
