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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 (转动的) 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 answer is , as some children said ,to have no homework at all.
1. From the passage we can learn that ______. [ ]
A. only children in China carry too heavy school bags
B. children in other countries don't carry too heavy school bags
C. both children in China and the US carry too heavy school bags
D. only children in the US carry too heavy school bags
2. Children feel it hard for them to go upstairs because ______. [ ]
A. they are too young
B. their school bags are too heavy
C. they don't know how to go upstairs
D. their parents don't always go upstairs with them
3. If a child carries a heavy school bag, ______. [ ]
A. his back and neck will be hurt
B. his head and arms will be hurt
C. his hands will be hurt
D. his feed will be hurt
4. According to the doctor, Scott Bautch, if a child in Grade 5 weigh about 30 kilos, the school bag he carries
should not be over ______. [ ]
A. 5 kilos
B. 3 kilos
C. 5.5kilos
D. 4.5 kilos
5. Some students thinks the best answer to this problem is that ______. [ ]
A .they should have a little homework to do after they got home
B. their teacher had better not ask them to do any homework
C. they should only take home library books they will read at night
D. they should use thin workbooks instead of thick books
（2）工业合成氨的热化学方程式为：N2（g）+3H2（g） 2NH3（g）；△H=-92.2kJ/mol。