Question: How useful to historians looking for evidence of social structure in the ancient river valley civilizations would the excerpts from the early law
codes?

Very useful for the historians.

Explanation:

It is very useful to historians looking for the evidence of social structure in  the ancient river valley civilizations because in these ancient river valley civilizations, there are a lot of evidences present about the social structure of the people living in ancient times. For evaluating the social structure of ancient river valley civilizations, the historians have to find out the evidences from the valley where the civilization lives.

it the big letter b heart my answer

the name of the theory is landmass theory.