C) power of television's influence in American politics.
Okay, well a plow is used for farming. Basically the Sumerian plow is like a modern day tractor. If you have ever heard the term, "to plow the fields", you would know and immediately think of a tractor.
It was the Mayans who built an ancient civilization, in what is now Mexico and Central America. They had an incredibly advanced civilization but were overcome by European settlers.
The lord would provide to the vassal land from which they could make money from and in return the vassal would contribute troops to the lords army. Sometimes vassals would also pay a small fee of grain or various other goods as a sort of tax for the land.