A、Because many things change quickly in the 21st century. B、Because writers are out of date. C、Because sometimes the date of pub

There are several ways you can find out about the countries and places you wish to visit. You can talk to friends who have travelled to the places. Or you can go and see a colour film about them. Or you can read travel books.
    It would seem that there are three kinds of travel books. The first are those that give a personal, subjective account of travels which the author has actually made himself. If they are informative and have a good index then they can be useful to you when you are planning your travels. The second kind are those books whose purpose is to give a purely objective description of things to be done and seen. If a well-read, cultured person has written such a book then it is even more useful. It can be sorted as a selected guide book. The third kind are those books which are called "a guide" to some place or other. If they are good, they will, in addition to their factual information, give an analysis or an explanation. Like the first kind they can be inspiring and interesting. But their basic purpose is to help the reader who wishes to plan in the most practical way.
    Whatever kind of travel book you choose you must make sure that it does not describe everything as "wonderful", "excellent" or "magical". You must also note its date of publication because travel is a very practical affair and many things change quickly in the 21st century. Finally, you should make sure that the contents are well presented and easy to find.
Questions 19 to 21 are based on the passage you have just heard.
19. Which is not one of the ways to get to know about the places we wish to visit?
20. What type of people a writer should be if he is to write a travel book in an objective description?
21. Why we need to pay attention to the book’ s date of publication?