19  수수수 수수수 수수 수수수수 수수? / p.66                                     Reader’s Bank Level 6
          There are two types of food in our daily diet. One is acidic food such 
       as meat, grain, sugar and dairy products. The other is alkaline food, 
       which is mainly fruits and vegetables. 
         Eating too many acidic foods causes many health problems, just as 
       acidic rain damages plants. If acidic substances build up in your blood, 
       oxygen and nutrition cannot travel freely among your cells. If your cells 
       are not provided with oxygen and nutrition, they die or get sick. In fact, 
       many human diseases result from your body being too acidic.
        According to nutritionists, the ideal diet should be 80% alkaline foods 
       and 20% acidic foods. This diet will keep you a little alkaline, which is 
       the healthiest state. So why don’t you try eating more fruits and veg-
       etables?
   
    20  수수수 수수수 수수수수 / p.68                                            Reader’s Bank Level 6
         A couple in their 90s is getting forgetful, so their doctor advises them 
       to write things down to help them remember. That night, when the old 
       man is about to go to the kitchen for a drink, his wife asks him to get 
       her a bowl of ice cream. She gently reminds him, “Shouldn’t you write it 
       down?” He says, “No, I can remember it.” But before he turns to go, his 
       wife says, “Well, since you’re going anyway, I’d like some strawberries 
       on top. You’d better write that down.” He replies, “I’ve got it in my mind!” 
       She adds, “I’d also like chocolate syrup. Now I’m certain you’ll forget 
       that.”. At this word, he loses his temper and says, “I do remember that: 
       ice cream with strawberries and chocolate syrup.” He then hurries into 
       the kitchen. Twenty minutes later, he returns with a plate of bacon and 
       eggs. His wife stares at the plate for a moment and asks, “Where’s my 
       toast?”
   
    21  수수수수수수? 수수수수수 수수수 수!_1 / p.70                                  Reader’s Bank Level 6
          In  1999,  a  website  conducted an online poll to choose the best 
      school for computer science. But some students at Carnegie Mellon 
      and MIT played a trick. They used a computer program to vote auto-
      matically  over  and  over  again. As  a  result,  those  two  schools  got 
      more votes than any other school. Later, in order to stop this kind of 
      cheating,  some  people  came  up  with  a  test  program  called 
      CAPTCHA.
        CAPTCHA is a kind of word recognition test that is designed to tell 
      computers and humans apart. The words shown on the test screen 
      have strange shapes. Humans can recognize them, but computers 
      can’t. Visitors to a website are required to type in the words to prove 
      that they are really human. This way, CAPTCHA can prevent com-
      puter programs from playing tricks.  
   
    21  수수수수수수? 수수수수수 수수수 수!_2 / p.70                          Reader’s Bank Level 6
       As CAPTCHA is widely used, its forms continue to evolve. There is 
     now an audio CAPTCHA that reads texts out loud for the blind. A 
     more advanced one is a 3D CAPTCHA that displays characters or 
     numbers in 3D.