It is not obvious in some analyses, but it is important to note that economic profits include opportunity costs. The profit of an entrepreneur (normal profit) is usually positive, but economic profit can be either positive or negative (loss). That's why the opportunity cost is included: in a completely competitive market, when marginal cost equals marginal revenue, profit maximization or loss minimization conditions arise. If the market price is lower than the total average cost, which means that the economic profit is negative, the entrepreneur needs to compare the value of the loss and the average variable cost. If the business continues to operate, the negative economic profit must not be lower than the average variable cost, otherwise the entrepreneur would rather shut down the company than continue to take the loss. The value was originally derived from the special material system, the preordering movement of dissipative structure, and the "ordering energy" was the original "value". With the continuous evolution of human beings, "ordering energy" further developed into "generalized and orderly energy", which gradually became the real human value. In a word, the value is derived from the nature, and with the evolution of the human evolution, the development of the society, the development trend of value of ultimate principle is only the movement of the material world and labor of human society. At the time of. The shape of the car was similar to that of the "sedan" in ancient China, and was as glorious as the car. The car was then called a car. First car, its body modelling is basically used for the carriage, in the form of so called "horseless carriage" English name Sedan is refers to the European noble a luxury passenger carriage, decoration not only pay attention to, and it is enclosed, wind, rain and dust, and to improve the degree of safety. When it was introduced to the United States in the 18th century, it was only possible for rich people in a few big cities such as New York and Philadelphia to enjoy it. When ford introduced the model T model in 1908, the body was changed from open to closed, and its comfort and safety improved greatly. Ford referred to his "Closedcar" as Sedan. The famous ford model T is the best car in the world. Moment of torque