The type of document is a letter
The argument he used was that because he had lived in a territory where slavery was illegal, he could never again be enslaved. This was a doctrine that was recognized in common law for centuries in Europe.
The correct answer among all the other choices is Steam locomotive. This is the transportation development that had the greatest long-term impact on the American economy. Thank you for posting your question. I hope this answer helped you. Let me know if you need more help.
I belive the answer is Secondary Source. Becasue its a politcal cartoon and not a direct news source.