It is very important to have healthy teeth. Good teeth help us to chew our food .They also help us to look nice.
How does a tooth go bad? The __51begins in a little crack in the  enamel(琺瑯) covering of the tooth. This happens after germs and bits of food have__52  there. Then the decay slowly spreads inside the tooth. In the end, poison goes into the blood, and we may feel quite ill.
How can we keep our teeth__53 ? First, we ought to visit our dentist twice a year. He can fill the small holes in our teeth before they destroy the teeth. He can__53 __54 our teeth to check that they are growing in the right way. __55 , many people wait until they have toothache before they see a dentist. Secondly, we should brush our teeth with a toothbrush and fluoride(氟化物) toothpaste at least__56  a day—once after breakfast and once before we go to bed. We can also use wooden toothpicks to__57between our teeth after a meal. Thirdly, we should eat food that is__58 to our teeth and our body: milk, cheese, fish, brown bread, potatoes, red rice, raw vegetables and fresh fruit. Chocolate, sweets, biscuits and cakes are bad, especially__59 we eat them between meals. They are harmful because they__60 our teeth and cause decay.
51.  A. destruction     B. decay         C. fault        D. hurt 
52.  A. stored          B. collected     C. laid         D. piled 
53.  A. healthy         B. complete      C. effective    D. painless 
54.  A. observe         B. skim          C. watch        D. examine
55.  A. Unexpectedly   B. Certainly small    C.Unfortunately  D. Generally
56.  A. once            B. twice        C. three times  D. four times 
57.  A. drill           B. dig           C. clean        D. explore
58.  A. delicious       B. valuable      C. beneficial   D. meaningful
59.  A. what            B. how          C. whether       D. when 
60.  A. stick to        B. attach to    C. fix on        D. keep to 

51---60    BBADC   BCCDA  

51.decay的意思是“腐爛”。(牙齒)的腐爛開始于覆蓋在牙齒上的琺瑯層上的小裂紋。destruction的意思是“破壞”；fault的意思是“缺點”；hurt的意思是“受傷”。答案為B。 
52.collected在此為不及物動詞，意思是“聚集；堆積”。細菌和食物聚集在牙縫后，就會引起牙齒琺瑯層的破裂。store作不及物動詞的意思是“貯藏”；laid是及物動詞，意思是“放”；pile常和up連用，意思是“堆積”。答案為B。
53.healthy“健康的”，本篇短文討論的是保持牙齒健康的問題。B為“完全的”；C為“有效的”；D為“無痛苦的”，均不合文意。答案為A。 
54.“examine”表示醫(yī)生檢查身體(某一神經(jīng))，看牙醫(yī)的目的是讓他檢查我們的牙齒是否生長正常。observe的意思是“觀察”；skim的意思是“掠過”；watch的意思是“注視”。答案為D。 
55. 每年至少看兩次牙醫(yī)可以保證我們牙齒的健康。他們可以為我們補牙，檢查我們的牙齡是否生長正常。但是，不幸的是人們只在牙痛時才去看牙醫(yī)。而A表示“出乎意料地”；B表示“肯定小”；D表示“一般地”，均不合題意。答案為C。 
56.從后句once after breakfast and once before we go to bed可知。答案為B。 
57.clean為“使……干凈”。飯后使用牙簽的目的是清除牙齒之間的食物。drill的意思是“鉆”；dig的意思是“挖”；explore的意思是“探險”。答案為C。 
58.beneficial的意思是“有益的”。為了保持我們牙齒的健康，我們必須吃有益于牙齒健康的食物。delicious的意思是“好吃的；美味的”；valuable的意思是“有價值的”；meaningful的意思是“意味深長的”。答案為C。 
59.巧克力、糖果、餅干和蛋糕對牙齒有害，特別是我們在兩頓飯之間吃這些東西。注意這四個選項的語法功能：what, how和whether只能引導名詞性從句；而when既可以引導名詞性從句，也可以引導時間狀語從句。從句子的結(jié)構和意思都可判斷出是時間狀語從句，而不會是名詞性從句。答案為D。 
60.stick to的意思是“粘住”。巧克力、糖果、餅干和蛋糕會粘在我們的牙齒上，造成牙齒破裂，所以它們是有害的。attach to的意思是“附屬于”；fix on的意思是“固定在”；keep一般不和介詞to連用。答案為A。
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B
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