The law of diminishing marginal utility states that the marginal value derived from a unit decreases as its use increases. This explains the phenomenon where the use of capital (its marginal product) decreases or diminishes as its utilization increases.

A public good is both non-rival (a person's use does not prevent another person's use) and non-rivalrous (a person cannot be excluded from using it). The only good that fits this description is the online blog. 

A market or industry that is dominated by a small number of firms is called an oligopoly. By contrast, monopolies are dominated by one firm, duopolies are dominated by two firms, and perfectly competitive and monopolistically competitive industries have many firms competing with one another. 

An increase in the demand for pizza will increase its price and quantity, while a decrease in the supply of pizza will increase its price and decrease its quantity. Thus, the price of pizza will unambiguously increase, but the quantity can either increase or decrease, depending on which change has the greater effect on supply.

When two countries trade two goods with one another, they will trade the goods that they have a comparative advantage in producing. One nation can have an absolute advantage in the production of both goods, but each nation will still have a comparative advantage in producing one of the two goods. 

Monopolistic competition is a situation where firms sell products that are differentiated from one another. In this situation, firms can behave like monopolies in the short run and earn positive economic profits. However, they will revert to making zero economic profit over the long run. 

Patents, limiting the number of licenses available, and economies of scale can all hinder a firm's ability to enter the market. A patent prevents a firm from replicating a product that originated from another firm. A limited number of licenses can exclude firms who are unable to obtain licenses from entering the market. Economies of scale can prevent smaller firms from entering the market by making such an action cost-prohibitive. 

All of these are examples of factors of production, which are the inputs necessary for a production process. 

When both goods are perfect substitutes, the consumer is indifferent between the amount of consumption of the two goods. Thus, his/her indifference curves will be straight lines, because the rate of substitution between the two goods will be constant. 

In perfectly competitive markets, there are low barriers to entry (think of a food truck--all one needs in order to operate are a truck, fuel, cooking equipment, and a business license), homoegenous products (consider a farm--nearly all cucumbers are identical to one another), and a large number of firms (this is what makes the environment so competitive).

In monopolistic competition and oligopolies, products tend to be heterogeneous, and in a monopoly, there are extremely high barriers to entry.