I think it's A. Delhi Sultan, Ibrahim Shah Lodi
This is a personal question, which means that only you can answer it. However, I can give some examples that might help guide your work.
An example of a primary source that you might encounter in your own life is that of a news article. As this article is likely to be written by a reporter witnessing the events, it can be considered a primary source. On the other hand, an example of a secondary source would be a non-fiction book that talks about a historical event. This is because such a book would give a second-hand account of an event based on historical information.
People helped hide fugitive slaves along the Underground Railroad and wouldn't turn them over to slave catchers.
The assembly line would be my first choice.
