Grain is used to feed cattle and livestock because it is healthy, cheap, ethical, and easy to grow in some American climates. Grain is the easiest and most cost-efficient way to feed livestock.
B. The Inca empire was led by rulers who were believed to be gods.
I think that maybe people are saying different answers because there might have been many such laws. I will mention one example: the Diversity Visa Immigration: it means that people from Eastern Europe have a higher change of obtaining a visa due to a smaller population in the US than the western European Countries.
B - bodhisattvas in Mahayana Buddhism