The human body is a machine that can raise lots of interesting questions．Why，for example，are yawns（呵欠）contagious（传染的）？What's up with ice﹣cream headaches？ Here are answers to these and other questions about our bodies．

    Why do I get a headache when I eat ice cream too quickly？

    Scientists aren' t exactly sure what causes the brain freeze when we eat ice cream or other super﹣cold foods too quickly，though some believe it's the result of changed blood flow in the nervous stem．Blood vessels in the head tighten to stop the loss of body heat and then relax to let blood flow rise；that sudden rush of blood is what causes the headache．You can improve an ice﹣cream headache by rapidly rubbing your tongue across the roof of your mouth to help warm up things．

    What causes my stomach to make a low continuous noise when I'm hungry？

     Actually，your stomach makes noise whether you're hungry or full；you just hear it more clearly when you're hungry．Think of your digestive tract（消化道）as a really long tube lined with smooth muscle tissue． These muscles move food，fluids and gas through your digestive tract．　A　．It can make you feel embarrassed（尴尬的） but is nothing to worry about．

   Why do I blush when I'm embarrassed？

   When you're embarrassed，your brain releases a shot of adrenaline（肾上腺素），which makes your heart race and blood vessels become larger in size．All this happens to increase blood flow and oxygen delivery throughout the body in a fight﹣on﹣ flight reaction（对抗反应）．There are a lot of tiny blood vessels in your face，which turn noticeably redder from this sudden rush of blood．As for the actual function of blushing，researchers are still trying to find that one out．

     Why are yawns contagious？

    Have you ever yawned in front of someone，only to have them yawn right back？ It's a common thing but researchers don't have a good explanation for it．They do，however，know this happens only with humans and chimpanzees（ 黑猩猩）．A bigger question puzzling scientists is why we yawn at all It used to be thought that yawning showed that oxygen to the brain was not enough，but that's just a myth．A growing body of research now shows that yawning is nature's way of keeping our brains cool．

（1）What is the meaning of the underlined word tighten？　　．

A．变松

B．变紧

C．变短

D．变长

（2）Which of the following sentences can be filled in the blank？　　．

A．And that's what you're hearing when your stomach makes noise．

B And that's why you're so hungry when your stomach is empty．

C．And that's what makes you feel uncomfortable when you're full．

D．And that's how it makes a difference to your digestive tract．

（3）Which of the following statements is TRUE？　　．

A．There is no way for you to improve an ice﹣cream headache．

B．Researchers have found out the actual function of blushing．

C．Your stomach makes noise only when you are hungry．

D．Researchers don't have a good explanation for why yawns are contagious．

（4）What is the best title of the passage？　　．

A．Some Interesting Facts

B．Our Strange Body

C．Some Useful Discoveries

D．Our Amazing Feelings