Which of the following is considered a strong primary source for a research paper? a. internet b. almanac c. encyclopedia d. nonfiction book

This depends on which was produced during the event itself. This does mean that for sure almanacs and encyclopedias are out, considering they are often made after the fact. A nonfiction book could be it, but it depends on if it was written during that time, or if after. Internet is another highly possible answer, considering resources on it could be written during the time. It all depends. 

I would probably go with either nonfiction book or internet. 

I think it would be the internet. That is the modern source most people use right now. But it depends though.