Among most of the plains indians, how did a person achieve high social standing? answers: a. by raiding parties of white settlers b. by sharing c. by accumulating possessions d. by selling land

The answer is B. by sharing.
In plains indians, a figure who share the most resource for the members are seen as someone dependable that would take care of his/her own.
Because of this, this figure would be highly valued by other social group members and increasing their social standin.

B. by sharing.  
This question is almost a direct copy of a statement from the book "Making America: A History of the United States". On page 432, an excerpt from the last paragraph, states "among most of the Plains Indians a person achieved high social standing not by accumulating possessions but by sharing." Given that the question is an almost exact copy that statement from the book, there is no doubt that about the correct answer being "sharing".