Wich enable an oligopoly to from with in a market

                (TAKEN FROM A SOURCE NOT MY WORDS!)

 Costs of starting a competing business are too high.
This answer is correct because the whole idea of oligopoly is that only that company has the funds and or resources to run a business.
Competition can't join the market because it is too expensive and already dominated by that oligopoly. 

Hope this helped!

:)

Pretty bad i would assume.