What contains most of earth's mass?

If your talking about the inside of the earth rather than the top it will be mantle

high entry costs prevent new producers from entering the market.

explanation:

an oligopoly is a term used to clarify the structure of a particular market, industry, or organization. a market is considered oligopolistic or amazingly focused when it is shared between a few companies.

African americans at the time just came out of slavery and needed money to provide for there families. so they joined for the money mainly.