Hmm... your question is a bit too vague (since there were no options included) but I will answer it to the best of my ability... a secondary source is valuable for gaining context about history but is unreliable as evidence.
There are two sources I know of: primary sources and secondary sources.
A primary source is like a the Declaration of Independence, the Constitution, etc. Primary sources don't have the the immediacy of the original thing.
A secondary source is like a textbook, as it was written to add to the primary source, and maybe biased.
Other possible answers to your question are: encyclopedia, anthology, historical fiction/history novel.
I hope that helps! :)