The culture of the plains indians changed by:
a: the growth of trade with the iriquios
b: the introduction of horses by spanish
c: the cost of wars with the aztec
d: the formation of a government with the spanish

The correct answer is B) the introduction of horses by the Spanish.

The culture of the Plains Indians changed by the introduction of horses by the Spanish.

The Indians in the Americas did not have horses. These animals were brought by the Spanish conquerors. So when the Spanished conquered territories in the Americas, the use horses as they did in Spain. This really benefitted the Indians in many ways. The obvious one, transportation. Horse ride faster than any other known method by the Indians in the Plains. And they could carry more things that a human. Just let's remind that Aztec's servants used to run 500 kilometers from the city of Tenochtitlan(nowadays modern Mexico City) to the port of Veracruz, to bring Emperor Monctezuma fresh fish to eat.