You think it's " cool " to carry your backpacks and head out to school．But if you don' t know exactly how to choose，load，lift and wear them﹣these all﹣important accessories（配件）can be a pain in the back．Not to mention the neck，head and shoulders．

   Backpacks can influence your health．Carrying a heavy load improperly can lead to

poor body position；and even hurt the spinal column（脊柱）．This can cause muscle strain，headaches，back，neck and arm pain．

    For example，if it is carried on one shoulder，a heavy backpack forces the muscles and spine to balance the unequal weight．This may increase the possible back problems later in life．

    More than 50 percent of young people suffer back pain by their teenage years．Research shows that this could be mainly caused by improper use of backpacks．

   Here's some advice to help you carry backpacks comfortably and safely．

   Choose the right backpack．Forget leather（皮革）! It looks great，but it's far too heavy．Go for canvas（帆布）．Pick a pack that has two wide，adjustable，comfortable shoulder straps（带子），along with a hip or waist strap，and plenty of pockets．Make sure the pack fits properly and its size is suitable for the wearers body．

    Packing it properly．Only put in the pack what is needed for that day．It's a good idea to know what each object weighs．The total weight of the filled pack should be no more than 10 to 15 percent of the wearer's own body weight．Pack heaviest objects close to the body，and place little ones outside， away from the back．

    Putting the backpack on．Put the pack on a smooth surface，at waist height．Put on the pack，one shoulder at a time，then adjust（调整）the straps to fit comfortably．Remember when lifting a backpack， or anything，to lift using the arms and legs and to bend at the knee．

   The right way to wear a backpack，Both shoulder straps should be used，and adjusted so that the pack fits the body，without hanging to one side．Backpacks should never be worn over just one shoulder．You should be able to move your hands between the backpack and your back．The waist strap should also be worn．

   Take the above advice，and you may not complain back pain，numbness or weakness in your arms and legs any more．

（1）What could mainly cause some young people to suffer back pain by their teenage years？　　．

A．Too much homework．

B．Poor treatment for backs．

C．Improper use of backpacks．

D．Unhealthy sleep position．

（2）Which of the following does the writer suggest？　　．

①Choose leather backpacks because it looks"cool" to go to school．

②Pick a pack that its size is suitable for the wearer's body．

③Make sure the backpack contains only what is needed for that day．

④Pack heaviest objects close to the body，and place little ones outside．

⑤Put the pack on a smooth surface，above the waist height．

A．①②④

B．①③⑤

C．②③④

D．②③⑤

（3）If a boy weighs 40kg，how heavy should his filled backpack be at most？　　．

A．About 4kg．

B．About 6kg．

C．About 10kg．

D．About 15kg．

（4）What is the passage mainly about？　　．

A．Some problems that teenagers face in their study at school．

B．The suitable backpack material that you should choose．

C．The good influence that backpacks have on your health．

D．Some advice on how to carry backpacks comfortably and safely．