When were the first mounds built in the ohio river valley?

a. between 8000 b. c. and 500 b. c.
b. between 13000 b. c. and 7000 b. c.
c. between 900 a. d. and 1650 a. d.
d. between 800 b. c. and 1200 a. d.

the answer is D:  between 800 B.C and 1200 A.D.

Explanation:

The first mounds in Ohio River Valley were built during the Woodland period which was 800 B.C. until 1200 A.D. The Adena culture and the Hopewell culture both built mounds during this time period.

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