听力原文： 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 classified as a selective guide book. The third kind are those books which are called 'a guide' to some place or another. If they are good, they will, in addition to their factual information, give an analysis or an interpretation. Like the first kind they can be inspiring and entertaining. But their primary function is to assist 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 'marvelous'', 'fabulous' or 'magical'. You must also note its date of publication because travel is a very practical affair and many things change quickly in this century. Finally, you should make sure that the contents are well presented and easy to find. How many kinds of travel books are mentioned in the passage?