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 <em>primary source</em> is like a the Declaration of Independence, the Constitution, etc. Primary sources don't have the the immediacy of the original thing.
A <em>secondary source</em> is like a textbook, as it was written to add to the primary source, and maybe biased.
<em>Other possible answers</em> to your question are: encyclopedia, anthology, historical fiction/history novel.
I hope that helps! :)
</h2>