In 1934, professor rei, of the center for fluid mechanics, used model cars to measure the aerodynamic drag of various bodies in wind tunnels Historical costs differ from current values 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. The optimal combination of benefits and risks is the best combination of benefits and risks. If the benefit is certain, the risk is minimized; Marx's interest rate determinism is based on the source and essence of interest. Marx reveals that interest is a portion of the surplus that the capitalist who lends capital is divided from the capitalist who borrows the capital, and the profit is the transformation form of the surplus value.