Answer:
Correct answer is They substitute for the limited written records that describe the founding of Rome.
Step-by-step explanation:
First option is not correct as they are not giving us factual details, as we are not sure those things really happened.
Second option is also not correct as they were not created by historians at all.
Third option is also not correct. We have a lot material sources, but they are not giving us all the details that we need to reconstruct this events.
Last option is correct as we are using them to fill the holes that we have due to lack of written sources.