听力原文： According to recent surveys, a large number of Americans favor increasing the present 55-mile-an-hour speed limit. The current speed limit was set in the early 1970's when the U.S. faced its first crucial oil shortage. Sixty-five percent of the persons surveyed said that the law was out of date. They pointed to the relative safety of the American highway system and to younger people, rather than older adults. They are more likely to argue against retention of the legislation.
The debate is particularly important for those who live in the western states. Many of the large cities in the western part of the country are separated by thirty or forty hours of long, empty, straight roads. People from this area argue that the examples of countries like Australia and Germany should demonstrate that higher speeds are still safe and that speed is disproportionately blamed for traffic problems.
Most professional truck drivers favor a higher speed limit. They argue that they can get their goods to the marketplace faster if the speed limit is higher, and that is good for the economy. Since the successful implementation of the turbo- charged engine in modern trucks, it is quite possible for trucks to reach speeds twice the legal limit which they are currently allowed to travel. In the end, economic issues may help make the final decision.
Why was the speed limit set at 55 miles per hour in the first place？

A. The older people wanted it.
B. The voters decided on it.
C. Speeds above 55 were not safe.
D. The U.S. had a fuel crisis.