7

　　backpacks（背包）with two straps(带子) to carry them,

　　8

　　a number of other students choose rolling backpacks. But even with rolling backpacks,

　　9

　　up stairs and buses with them is

　　10

　　a problem for kids. Many of them have hurt their knees, backs or necks because of heavy school bags.

　　But how much is too

　　11

　　? Experts say students should carry

　　12

　　more than 10 to 15 per cent of their own body weight. Scott Bautch, a Wisconsin

　　13

　　doctor, said kids under 4th grade should

　　14

　　with 10 per cent. But it’s also important that older kids don’t go

　　15

　　15 percent, because their bones are still growing. Bautch explained that there are other injuries caused by backpacks. “Kids are

　　16

　　their balance and falling down with these backpacks,” he saiD．

　　Parents and teachers are starting to tell the kids to only take

　　17

　　library books they will be reading that night. Some teachers are using worksheets(作业纸) or

　　18

　　workbooks for students to take home.

　　One of the best answers is, as some

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