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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 from 44 to 50.

      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 to each of the questions from 39 to 43.

      It used to be that people would drink coffee or tea in the morning to pick them up and get them going for the day. Then cola drinks hit the market. With lots of caffeine and sugar, these beverages soon became the pick-me-up of choice for many adults and teenagers. Now drink companies are putting out so-called “energy drinks”. These beverages have the specific aim of giving tired consumers more energy.

      One example of a popular energy drink is Red Bull. The company that puts out this beverage has stated in interviews that Red Bull is not a thirst quencher. Nor is it meant to be a fluid replacement drink for athletes. Instead, the beverage is meant to revitalize a tired consumer’s body and mind. In order to do this, the makers of Red Bull, and other energy drinks, typically add vitamins and certain chemicals to their beverages. The added chemicals are like chemicals that the body naturally produces for energy. The vitamins, chemicals, caffeine, and sugar found in these beverages all seem like a sure bet to give a person energy.

      Health professionals are not so sure, though. For one thing, there is not enough evidence to show that all of the vitamins added to energy drinks actually raise a person’s energy level. Another problem is that there are so many things in the beverages. Nobody knows for sure how all of the ingredients in energy drinks work together.

      Dr. Brent Bauer, one of the directors at the Mayo Clinic in the US, cautions people about believing all the claims energy drinks make. He says,  “It is plausible if you put all these things together, you will get a good result.” However, Dr. Bauer adds the mix of ingredients could also have a negative impact on the body. “We just don’t know at this point” he says.

(Trích từ đề minh họa lần 1, 2017)

What is the main idea of this passage?

    A. Caffeine is bad for people to drink.

    B. It is uncertain whether energy drinks are healthy.

    C. Red Bull is the best energy drink.

    D. Teenagers should not choose energy drinks.