Primary sources are valuable to historians because they give insight into the ways in which historical figures understood or internalized what they experienced, their place or significance in history, and give historians an understanding of historical figures' opinions.
I believe the answer is: Reference group
Reference group refers to the group that become subjects of comparison to another group of individual.
Most people use this reference group to measure our own worth (for example, if you want to know whether you a bad or good guitar player, the reference group that you would most likely use would be famous band member) , and this might influence the formation of our identity in the future.
Answer:
A. Missouri River
Explanation:
Missouri River=2,341 mi (the longest)
Red River =1,360 mi
Arkansas River=1,469 mi
Rio Grande River=1,885 mi
