Your best answer is D) out of all of them.
Yes, Artifacts is important in giving historical evidence and context, but it in itself is an enigma, and must be understood in itself. What was the purpose of such an artifact being made? Did it have a practical usage, or was it only a ceremonial, or at best, something used when lightening the mood (so to speak).
Ancient Materials include a wide variety of things, and some can be used for specific historical understanding. You need to choose the right materials to create the right understanding as well as well-grounded thesis for how a civilization or historical people-group function. You cannot just find a arrow, and state that the civilization only used arrows and no other weapons. In fact, it may be fool-hardy for such to occur, as it causes generalization and failure to get the big picture. Granted, A.M. is needed to back up the history, but at the end, it is only a tool in helping us understand our history better.
Past and current sources can be a extremely nice (and easier) way to find information, but it does not not come with it's own problems. One extreme problem is the highly-opinionated and heavily influenced writing, in which the author's belief's and mindset can drastically influence how the reader would then take into account what is happening. For example, a European writer on the Native Americans may describe them as war-mongers, godless heathens, uncivilized fools, and below-human standards. But to step away from the source, we should first look at the perspectives of both groups, and then look to see if that particular source does justice to all sides of the party. The important question here is: Who is writing? What are the parties in the writing, and is the author affiliated to one or the other party? How was the author brought up? Where are the sources of information from? Remember, one cannot truly know all the information surrounding an event, and there will always be newly discovered evidence that can suggest otherwise.
Reliable Documents are documents that have been proven through historical evidences on the site, and can be used to give a factual (but may still be opiniated-influenced source) of what has occurred during the event. it is the best choice out of all of them, but remember to take opinions with a grain of salt.