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    Modern life is impossible without traveling. The fastest way of traveling is by plane. With a modern airliner(客机), you can travel in one day to places which needed a month or more to get to hundreds of years ago.
    Traveling by train is slower than by plane, but you can see the places you are traveling through. Modern trains have comfortable seats and dining-cars. They even make the longest journey enjoyable(令人愉快的).
    Some people prefer to travel by sea. You can visit many other countries or different parts of your country. Ships are not so fast as trains or planes, but traveling by sea is a very pleasant way to spend a holiday.
    Many people like to travel by car. You can make your own timetable. You can travel three or four hundred miles or only fifty or one hundred miles a day, just as you like. You can stop if there is something interesting, for example, at a good restaurant where you can enjoy a good meal, or at a hotel to spend the night. That’s why traveling by car is popular for pleasure trips, while people usually take a train or a plane when they travel on business.

匀加速直线运动中，加速度为3 m/s²，则（  ）