The correct answer is C) the Spiro mound builders.
The prehistoric culture that built 12 mounds by hand between 850 and 1450 CE was the Spiro mound builders.
The Spiro Mounds are located in Le Flore County, close to Fort Smith, Arkansas. The place is located on the southern bank of the Arkansas River. It is a Prehistoric American Indian site that built mounds in this ceremonial complex. The Spiro tribe was part of the Mississippi culture that inhabited the place from 800 AD to 1450.