A、Encourage the growth of reading. B、Change people’s attitudes to reading. C、Show how reading methods have been improved. D、Expl

Reading to oneself is a modern activity which was almost unknown to the scholars of the classical and medieval worlds, while during the fifteenth century the term "reading" undoubtedly meant reading aloud. Only during the nineteenth century did silent reading become commonplace.
    One should be careful, however, in assuming that silent reading came about simply because reading aloud is a distraction to others. Examination of factors related to the historical development of silent reading reveals that it became the usual mode of reading for most adult reading tasks mainly because the tasks themselves changed in character.
    The 19th century saw a steady gradual increase in literacy, and thus in the number of readers. As readers increased, so the number of potential listeners decreased, and thus there was some reduction in the need to read aloud. As reading for the benefit of listeners grew less common, so came the flourishing of reading as a private activity in such public places as libraries, railway carriages and offices. There reading aloud would cause distraction to other readers.
    Towards the end of 20th century there was still considerable argument over whether books should be used for information, and over whether the reading material such as newspapers was in some way mentally weakening. Indeed this argument remains with us still in education. However, whatever its virtues are, the old shared literacy culture had gone and was replaced by the mass media on the one hand and by books and magazines for a specialised readership on the other. The social, cultural, and technological changes in the century had greatly altered what the term "reading" implied.
Questions 16 to 19 are based on the passage you have just heard.
16. Why was reading aloud commonplace before the 19th century?
17. What did the development of silent reading during the 19th century indicate?
18. What are educationalists still arguing about?
19. What is the speaker attempting to do?