Ⅲ.综合运用

The Science of Tooth Brushing

For many people,the first thing they do after waking up in the morning is to brush their teeth.Here comes the question:Before brushing your teeth,do you dip your toothpaste in water?Most people may not even notice this h__1__movement,but it does a__2__your dental health.

As a matter of fact，it is i__3__to dip your toothpaste in water before brushing your teeth.If the toothpaste is stained with water，its cleaning e__4__may be weakened.A dip into water makes it easier to foam（起泡），so people might s__5__their tooth-brushing time and leave more food residue（残渣）and bacteria（细菌）between their teeth.The proper length of time for tooth brushing should be around two to three minutes.

It is the friction（摩擦）b__6__teeth，toothbrush and cleaning ingredients（成分）in the toothpaste instead of the foam that cleans your teeth.Therefore，it is a__7__not to dip toothpaste in water before you brush your teeth.

1.h____________2.a____________3.i____________4.e____________5.s____________6.b____________7.a____________