Suppose a market has only two consumers - Consumer A and Consumer B, and two producers - Producer A and Producer B. Which identity is a useful way to describe equilibrium in a perfectly competitive market?

	a.	price = marginal cost to producer B
	b.	marginal benefit to Consumer A > marginal benefit to consumer B
	c.	price = marginal benefit to Consumer A
	d.	price = marginal benefit to Consumer A = marginal benefit to consumer B = marginal cost to producer A = marginal cost to producer B