When the demand for something is greater than its supply, producers and suppliers will sense the possibility of making a profit – the excess of revenues over expenses is the profit.
As the case illustrates, competition takes four general forms: pure competition, monopoly, monopolistic competition, and oligopoly(少数制造商对市场的控制).
The classic example of pure competition occurs with a commodity, like wheat or corn, that has so many producers that no one of them can control its selling price.
A monopoly occurs when one company alone offers a particular food or service and therefore controls the market and price for it.
Private restaurants serve gourmet food for $70 per person; incentives boosted agricultural production 25 percent and industrial output 80 percent in just three years; farmers are encouraged to raise as much as they can on their own plots, and some become almost rich in the process.(注意本句中分号的使用)