The answer is A (Jan Ernst Matzeliger)
A. Computers.
People find the research and store it on documents and internet so it is A. Computers.
It is true that you can have contradicting personalty
Nebraska was too far north for plantations--people of Nebraska wanted territory without slavery. Kansas was further south and platations could be built there. As soon as the Kansas-Nebraska Act was passed, thousands of people rushed to claim land in Kansas. This would tip the vote on slavery.