A、Check your number and call again. B、Tell the operator what has happened. C、Ask the operator to put you through. D、Ask the oper

Telephone books in the United States have white, blue and yellow pages. The white pages list people with phones by last name, the blue pages contain numbers of city services, government agencies and public schools. Businesses and professional services are listed in a special section: see the yellow pages. To make a long-distance call, you need an area code. Each area in the U.S. has an area code. The area covered by one area code may be small or large. For example, New York City has one area code, but so does the whole state of Oregon. If you want to know the area code of a place, you can look it up in the area code map, which is printed in the front of the white pages.
   There are a lot of public telephones in the U.S. They have their own numbers. If you are making a long-distance call on a public telephone and run out of money, give the number on your phone to the person you are talking to, then hang up the receiver, and he can call you back. If you make a long-distance call and get a wrong number, call the opera tor and explain what happened. This means that you can make the call again to the right number without having to pay more money.
   Questions 19 to 21 are based on the passage you have just heard.
   19. Where can you find the telephone number of a city council in the telephone book?
   20. Where can you find an area code map of the U.S.?
   21. What are you advised to do when you get a wrong number in making a long distance call?