Are you carrying too much on your back to school? I'm sure lots of your age will say "Yes". Not only the students in China have this problem, but children in the United States also have heavy school bags.  Doctors are starting to worry about that younger and younger students are having problems as a result of school bags being too heavy for them. "It's hard for me to go upstairs with my bag because it's so heavy," said Rich Hammond, an 11-year-old student in the US. Rich is among students who have common school bags with two straps to carry them, but many other choose rolling   bags. But even with rolling bags, getting up stairs and houses is still a problem for children. Many of them have hurt backs and necks because of the heavy school bags. But how much is too much? Doctors say students should carry no more than 10% to 15% of their own body weight. Scott Bautch, a black doctor, said children under Grade 4 should stay with 10%. But it is also important that older children don't stay with over 15%, because their bodies are still growing. "Children are losing their balance and falling down with their school bags," he said. Parents and teachers are starting to tell children to only take home library books that they will be reading at night. Some teachers are using pieces of paper or thin workbooks for students to take home.  One of the best answers is, as some children said, to have no homework at all. If a child carries a heavy school bag,   _   .
his back and neck will be hurt his head and arms will be hurt his hands will be hurt his feed will be hurt