There are more than 100 million cars in the United States. A normal car gets less than 15 miles from each gallon of gas. It travels about 10,000 miles each year. In that time, it uses about 650 gallons of gas. In all, autos use up some 70 billion gallons of gas a year. That comes out to be four-and-a-half million barrels a day. The importance of saving gas, then, cannot be stressed too much. Let's say, for instance, that the fuel used by each car could be cut back just 15 percent. This could be done by making fewer trips each day. It could be done through better driving habits. If it were done, our nation's use of fuel would fall by close to two-thirds of a million barrels per day. We can all help save gas. One way is to ride the buses. Some of us could walk to work. We could ride mopeds(机动脚踏两用车) or bikes. Another way is to share a ride. We could join carpools (合伙使用汽车). About one-third of all cars are used for going to and from work. Go shopping with a friend from time to time. If two people use a car instead of one, we all save. There would be fewer cars on the road. The savings on gas around the nation would come to more than one half million barrels a day. Another way to save is by cutting our useless trips. Can you find one car trip per week that could be handled by telephone? Can you combine trips? If each car took one less 10-mile trip a week, we could save three-and-half billion gallons of gas a year. This comes to nearly 5 percent of the total passenger car demand for gas. The way people drive decides how much fuel they save. Careful drivers may get20 percent more miles per gallon than normal drivers. They could get 50 percent more miles per gallon than wasteful drivers. Careful drivers obey the 55-mile-per-hour speed limit. They get to their desired speed quickly and keep a steady pace. If just one gallon of gas were saved each week for each car in the country, we could all save about five-and-half billion gallons a year. To decrease the number of useless car trips, you can use the ______.