Only "large" firms are able to sell __________ securities, with __________ yields than the securities the small and mid-size firms can sell

At equilibrium, quantity sold equals the quantity bought. This implies that

A) to sell more, producers require more in payment than consumers are willing to pay. B) government regulation is necessary. C) to sell less would require a lower price but would yield greater profit. D) those who don't buy have been treated unfairly.

What is the difference between sunk costs and marginal costs?