Answer: A
Explanation:
Among all the given statements the one which is not true in the context of the Mound Builders is that their culture flourished for 6,000 years. Hence, Option B is correct.
Among all the given statements the one which is not true in the context of the Plains Indians is that they lived in a flat, rolling, grassland region. Hence, Option D is correct.
Who are the Mound Builders?The tribe which is known as prehistoric American Indians are the Mound builders. They received this name because of the activities which were performed by them.
Such activities include the practice of burying their dead in large mounds. They came into existence about three thousand years ago. They are the ones who were responsible for building some extensive earthworks.
Thus, Option B for part A and Option D for part B is correct.
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