Market structures differ on two important dimensions:
a) price discrimination and product differentiation.
b) number of sellers and product differentiation.
c) surplus maximization and number of sellers
d) price discrimination and surplus maximization

b) number of sellers and product differentiation.

Explanation:

Market structures are used to evaluate the economic environment of a business. There are four main  market structures namely; oligopoly, perfect competition, monopoly and imperfect competition. They are differentiated by two main factors; number of sellers in the market and how the product offered in the market is differentiated. For example in perfect competition, there are many buyers and many sellers whereas in monopoly, there is a single seller and many buyers.

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explanation:

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it's obviously d. it could be c though.