The correct answer is C) a historian for the website of Sioux tribe of Montana.
The source that would most likely provide expert information on the Sioux tribes of Montana from 1800 to present day is a historian for the website of Sioux tribe of Montana.
The historian that works for the official website of the Sioux tribe of Montana has the most exact information because he works with Sioux people that know their history and live the culture and traditions of the Sioux tribe. He/she handles first-hand information and has access to research or ask any specific detail. A middle school teacher of Historian professor cannot have this direct access and one way or the other are going to use the Sioux official web site to collect the information needed.
