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Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions. The cause of tooth decay is acid, which is produced by bacteria in the mouth. The acid removes minerals from tooth enamel, allowing tooth decay to begin; the saliva in your mouth encourages remineralization and neutralizes the acid. The rate at which bacteria in the mouth produce acid depends on the amount of plaque on the teeth, the composition of the microbial flora, and whether the bacteria of the plaque have been "primed" by frequent exposure to sugar. To keep your teeth healthy, a regular dental hygiene program should be followed.Removing plaque with a toothbrush and dental floss temporarily reduces the numbers of bacteria in the mouth and thus reduces tooth decay. It also makes the surfaces of the teeth more accessible, enabling saliva to neutralize acid and remineralize lesions. If fluoride is present in drinking water when teeth are forming, some fluoride is incorporated into the enamel of the teeth, making them more resistant to attack by acid. Fluoride toothpaste seems to act in another way, by promoting the remineralization of early carious lesions.In addition to a regular dental hygiene program, a good way to keep your teeth healthy is to reduce your intake of sweet food. The least cavity-causing way to eat sweets is to have them with meals and not between. The number of times you eat sweets rather than the total amount determines how much harmful acid the bacteria in your saliva produce. But the amount of sweets influences the quality of your saliva. Avoid, if you can, sticky sweets that stay in your mouth a long time. Also try to brush and floss your teeth after eating sugary foods. Even rinsing your mouth with water is effective.Whenever possible, eat foods with fiber, such as raw carrot sticks, apples, celery sticks, etc., that scrape off plaque, acting as a toothbrush. Cavities can be greatly reduced if these rules are followed when eating sweets. What does this passage mainly discuss?
Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer for each of the blanks. The ability to weep is a uniquely human form of emotional response. Some scientists have suggested that human tears are (1) _____ of an aquatic past, but this does not seem very likely. We cry from the moment we enter this world, for a number of reasons. Helpless babies cry to persuade their parents that they are ill, hungry or uncomfortable. As they (2) _____, they will also cry just to attract parental attention and will often stop when they get it. The idea that having a good cry do you (3) _____ is a very old one and now it has scientific validity since recent research into tears has shown that they (4) _____ a natural painkiller called enkaphalin. By fighting sorrow and pain, this chemical helps you feel better. Weeping can increase the quantities of enkaphalin you (5) _____. Unfortunately, in our society, we impose restrictions upon this naturally (6) _____ activity. Because some people still regard it as a (7) _____ of weakness in men, boys in particular are admonished when they cry. This kind of repression can only increase stress, both emotionally and physically.Tears of emotion also help the body (8) _____ itself of toxic chemical waste, for there is more protein in them than in tears resulting from cold winds or other irritants. Crying comforts and calms can be very enjoyable - (9) _____ the popularity of highly emotional films which are commonly (10) _____ “weepies”. It seems that people enjoy crying together almost as much as laughing together.