Ⅲ.综合运用

Having an Itch

Many things can cause your skin to itch.Bug bites，dust，hair and skin problems are just some of the many c__1__of itching.When your brain senses an itch，what does it tell your body to do？Scratch（挠）！

The natural r__2__to an itch is to scratch it with your fingernails.For example，if you are bitten by a m__3__，the bite will cause an itchy feeling.Scratching can temporarily relieve（缓和）the itch.Why is that？

Scratching the skin causes a small pain reaction.Generally,the area of skin a__4__by an itch is quite small.When we scratch the itch,we might scratch a much larger area of skin.The pain caused over a larger area of skin distracts us from the itchy feeling,p__5__temporary relief.

Meanwhile，scratching causes the brain to r__6__serotonin（血清素）.The chemical is related to pain relief.Scientists believe serotonin may also make itching worse.It helps explain why scratching only provides temporary relief and itching can be worse a__7__scratching.

1.c____________2.r____________3.m____________4.a____________5.p____________6.r____________7.a____________