Are you carrying too much on your back at school? You’re not alone. Back experts in the United States are worried that young students are having back and neck problems as a result of carrying too much in their backpacks (schoolbags)
“It hurts my back when I run,”said Oberlin Reyes, a student in Virginia. “It’s hard to go up the stairs with my backpack,because it’s too heavy,”
Oberlin was among students whose backpacks were weighed for a week in a recent study.
They had regular backpacks with two straps(带子)to carry them, but a number of students with heavy loads had switched to rolling backpacks (which have wheels and can roll on the ground).
Shirley Park, whose backpack weighed 10 kilograms,said she changed to a rolling backpack because she was starting to have back  pain.
How much is too much?Experts say students should carry no more than 10 to 15 percent of their own body weight.
A few students had one suggestion to lighten the load:less homework.
P.S.( 附)Doctor’s suggestion:
1 Lighten the load. Clean out binders(活页材料)and take home only the books you need that night.
2 Wide straps are better. They send out the weight over your shoulders more evenly(均匀)。 And be sure to wear both straps rather than hanging the pack over one shoulder.
3. Pack smart. The heavier things should be packed closed to the back.
4.Bend both knees when you pich up the pack ,and don’t just bend over  at the waist.(腰)
“_________”is the main idea of the text.
A The problem of backpacks is worth studying.
B The problem made by heavy backpacks
C What is the best backpack for a student.
D      How to make students’backpacks light.
According to Oberlin Reyes and Shirley Park, we know________.
A students have to do too much homework
B students have to carry several backpacks
C backpacks without wheels are bad for students
D too much homework leaves students no free time
The expression “switched to” in the text perhaps means________.
A started to use  B turned to  C caught up   D used for
According to the passage ,it’s better for a student of 40 kilograms to carry a backpack of _____at most by the words of experts.
A 10kg    B 8kg  C 6kg    D 7kg
If students follow the doctor’s suggestions they ________.
A may lighten their backpacks
B can learn how to help themselves
C may feel their backpacks are lighter
D will know how to wear backpacks