题目

阅读下面的短文，请根据短文后的要求答题(请注意问题后的字数要求)。 In the United States, train transportation is unpopular compared with cars and airplanes. Most people like traveling by car or by air. Officials of the United States Department of Transportation made a study in 2001. The study is about how many miles Americans traveled by different means of transportation. They only studied trips longer than 50 miles. The study showed that fifty­six percent of all miles were traveled in personal vehicle. Forty­one percent were traveled in an airplane. Two percent 函数的自变量x的取值范围是    ．