B, handwritten letters, because the letters are probably the most credible, especially since they're a first-hand account of things that happened to your ancestors, and as WorldlyGlass45 mentioned in their answer to this question on another post, you'll most likely get the most info from the letters as well.
The reason that we receive education is so that we can get jobs and invent new things. If the people during the Industrial Revolution did not have any knowledge they would not have been able to create any of the inventions that were made. Therefor, the US and many other places inspired by these inventions would be completely different. This is just an example.
I hope this helps!
