All of the following led to the defeat of the plains indians except:
a. the colt six-shooter
c. the battle of little big horn
b. winter campaigning
d. the loss of their main food source, the buffalo

All if the following led to the defeat of the Plains Indians except C. the Battle of Little Bighorn. That Battle was actually a resounding success for the Plains Indians led by Crazy Horse. In that battle, the Sioux, Cheyenne, and other tribes defeated the 7th Cavalry and killed George Armstrong Custer. Of course, while this was a success, the US Army increased its pacification efforts thereafter.

The answer is c. good luck : )