Answer:
B. An oligopoly
Step-by-step explanation:
An oligopoly is characterised by a few firms operating in an industry. The babysitters came together to set price in collusion. Collusion is a characteristic of an oligopoly.
Also the babysitters set the market price for their goods. This is a characteristic of an oligopoly.
A purely competitive industry is when there are many buyers and sellers of homogenous goods and services. Firms are price takers. They have no influence over the market price. Price is set by the forces of demand and supply.
A monopoly is when there is only one firm operating in an industry.
A monopolistic competition is when there are many buyers and sellers of differentiated goods. Firms set the market price of their good.
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