There are many firms in both perfect competition and monopolistic competition

Costs must be kept as low as possible in both monopolistic competition and monopoly

There may be homogeneous products in both perfect competition and oligopoly

There are barriers to entry in both oligopoly and monopoly

They help to make a market contestable

They may include a fear of sunk costs

They may include a lack of know-how

They may include the well-known brand names of existing firms

A perfect competitor has no influence over the price of its product

A monopolistic competitor may engage in non-price competition

An oligopolist may monitor the prices and products of all the other firms in its market

A monopolist must be a large firm.

The depreciation on the bus

The wage of the job you gave up

The fuel you buy for the bus

The interest you earned on your savings before you used them to buy the bus

Its explicit costs only

Its explicit costs plus depreciation

Its implicit costs only

Its explicit costs and its implicit costs