Are you carrying too much on your back at school? You're not alone. Back experts in the USA were worried that young students are having back and neck problems because they are carrying too much in their backpacks (schoolbags). "It hurts my back when I run," said Eglin Reyes, a student in Virginia. "It's hard to get up the stairs with my backpack because it's too heavy." Students have to carry heavy backpacks on their backs for a whole week's study. Beeline is one of them. They have regular backpacks with two straps  to carry them, but a number of students with heavy loads have switched to rolling backpacks. The backpacks have wheels and can roll on the ground. Shirley Park's backpack weighs 10 kilos, and she said, "I'll change to a rolling backpack because I am starting to have back pain." How much is too much? Experts say that students should carry no more than 10 to 15 percent of their own body weight. A few students have had a good idea to lighten the load: Less homework. Doctor's suggestions: *Lighten the load. Take home only the books the students need that night. *Wide straps are better. They can send out weight over your shoulders and be sure to wear backpacks with two straps. *The heaviest things should be packed closest to the back. *Bend  both knees when you pick up the pack, don't just bend the waist . The main idea of the passage is about   _  .
the problems made by rolling backpacks the advantage of backpacks the best backpacks for students how to lighten students' backpacks
Question: Are you carrying too much on your back at school? You're not alone. Back experts in the USA were worried that young students are having back and neck problems because they are carrying too much in their backpacks (schoolbags). "It hurts my back when I run," said Eglin Reyes, a student in Virginia. "It's hard to get up the stairs with my backpack because it's too heavy." Students have to carry heavy backpacks on their backs for a whole week's study. Beeline is one of them. They have regular backpacks with two straps  to carry them, but a number of students with heavy loads have switched to rolling backpacks. The backpacks have wheels and can roll on the ground. Shirley Park's backpack weighs 10 kilos, and she said, "I'll change to a rolling backpack because I am starting to have back pain." How much is too much? Experts say that students should carry no more than 10 to 15 percent of their own body weight. A few students have had a good idea to lighten the load: Less homework. Doctor's suggestions: *Lighten the load. Take home only the books the students need that night. *Wide straps are better. They can send out weight over your shoulders and be sure to wear backpacks with two straps. *The heaviest things should be packed closest to the back. *Bend  both knees when you pick up the pack, don't just bend the waist . The main idea of the passage is about   _  .
A. the problems made by rolling backpacks
B. the advantage of backpacks
C. the best backpacks for students
D. how to lighten students' backpacks
Answer: