Enlightenment thinkers questioned traditional ideas
a.) government
b.) medicine
c.) religion
d.) science

Enlightenment thinkers questioned traditional ideas about "government", since they began to question the status quo regarding a monarch's legitimacy and ability to rule strictly because of a bloodline. This type of thinking was very influential for the Founding Fathers of the United States. 

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.