The United States has about 475,000 school buses -- all painted yellow. Each day they carry more than 25,000,000 children, half of all schoolchildren in the country. But these buses, on average, use four liters of diesel (柴油) fuel to travel less than sixteen kilometers. When the school year began last fall, diesel averaged 55 cents a liter nationally. The price nearly doubled, to a dollar and 8 cents, by the end of school in June.
Bob Riley speaks for the American School Bus Council. He says fuel prices for schools arc not much lower than others have to pay. As a result, schools are looking for ways to reduce transportation costs. Bus routes are being redrawn or, in some cases, canceled. Some areas are buying buses that use natural gas or other alternative fuels. Other steps include fewer field trips and less travel by sports teams. And some school districts may end any bus service not required by law.
Studies show that school buses are the safest form of transportation to and from school. The American School Bus Council says cuts in bus service are bad for children and possibly the environment. It says removing buses from the road will mean an increase in other vehicles transporting students. Spokesman Bob Riley says another concern is that reducing bus services might reduce attendance.
But it could also get more children to walk or bicycle to school. And that would surely make people happy at the National Center for Safe Routes to School. More kids walking or biking safely to school is the aim of a three-year-old federal program, part of an international movement. The goal is to increase physical activity and reduce air pollution. The United States will celebrate Walk to School Day on October eighth this year. But for some students, high fuel prices could make every day a walk-to-school day.
68. What does this passage mainly tell us?
A. High fuel prices' influences on school buses.  B. New measures to transport school students.
C. The safest form of student transportation.          D. The origin of Walk to School Day.
69. Which of the following information is implied in the first paragraph?
A. There are too many school buses in the United States.
B. There are too many students in the US.  
C. Diesel prices are going up too rapidly in the US.
D. School buses consume too much diesel in the US.
70. In order to cut down transportation cost, many schools take the following measures EXCEI _____.
A. changing some bus routes                B. stopping some bus routes
C. asking parents to drive children to school     D. using other types of fuels
71. The National Center for Safe Routes to School encourages more children to walk or bike to school in order to ________.
A. save more fuels and diesel for the country.
B. keep the children safe on their way to school
C. make the children live a simple life
D. keep the children healthy and the environment clean