用一张已除去表面氧化膜的铝箔紧紧包裹在试管外壁（如图），将试管浸入硝酸汞溶液中，

How to protect your teeth
    小题1:    . The first of twenty being to grow when you are over six months old. The second set of thirty-two grows from the age of six until you are about twenty-one years old.
   小题2:    , you must drink plenty of milk and eat greens.
    小题3:   . Then little food will be left on or between them to cause decay(导致蛀牙). Make sure that you turn the brush and go up and down as well as brushing side ways. Use dental floss(牙线)to make sure all food is removed from in between each tooth, if you cannot brush your teeth after eating, raise them with water, or eat an apple or a carrot.
    小题4:  . If there is a hole in a tooth, he or she will fill it. If you do not have it filled, then the hole will grow larger. When a hole grows too big,     小题5:  . It is better to keep all your second set of teeth for as long as possible. Filling a gap where a tooth has come out with a kind of bridge and using a false tooth costs a lot of money.

A. To help your teeth grow strong. B. You should brush your teeth after each meal. C. Carrots and apples are good for your teeth. D. The tooth may have to be taken out. E. Everyone should have a set of good teeth. F. Try to visit a dentist every six months. G. Every person has two set of teeth.