As cultural symbols go, the American car is quite young. The Model T Ford was built at the Piquette Plant in Michigan a century ago, with the first rolling off the assembly line（装配线） on September 27, 1908. Only eleven cars were produced the next month. But eventually Henry Ford would build fifteen million of them.

Modern America was born on the road, behind a wheel. The car shaped some of the most lasting aspects of American culture: the roadside diner, the billboard, the motel, even the hamburger. For most of the last century, the car represented what it meant to be American-going forward at high speed to find new worlds. The road novel, the road movie, these are the most typical American ideas, born of abundant petrol, cheap cars and a never-ending interstate highway system, the largest public works project in history.

In 1928 Herbert Hoover imagined an America with "a chicken in every pot and a car in every garage." Since then, this society has moved onward, never looking back, as the car transformed America from a farm-based society into an industrial power.gkstk

The cars that drove the American Dream have helped to create a global ecological disaster. In America the demand for oil has grown by 22 percent since 1990.

The problems of excessive（过度的）energy consumption, climate change and population growth have been described in a book by the American writer Thomas L. Friedman. He fears the worst, but hopes for the best.

Friedman points out that the green economy（经济）is a chance to keep American strength. "The ability to design, build and export green technologies for producing clean water, clean air and healthy and abundant food is going to be the currency of power in the new century."

28. Why is hamburger mentioned in paragraph 2?