[C] Why the torch towers were built.

　　[D] How the Great Wall came into being.

　　Questions 19 to 22 are based on the conversation you have just heard.

　　19. [A] By attending a class. [B] From her parents.

　　[C] Through a gardening magazine. [D] From her neighbors.

　　20. [A] Sunlight. [B] Location. [C] Soil. [D] Drainage.

　　21. [A] Tomatoes, beets, eggplant, and cabbages.

　　[B] Strawberries, green peppers, and okra.

　　[C] Basil, onions, cantaloupe, and banana peppers.

　　[D] Green beans, bananas, corn, and pumpkins.

　　22. [A] You can grow vegetables vertically.

　　[B] You can raise plants in a confined area.

　　[C] You can plant a wide variety of plants together.

　　[D] You can enjoy the beautiful scenery.

　　Questions 23 to 25 are based on the conversation you have just heard.

　　23. [A] E-commerce. [B] Wireless communications.

　　[C] Business and the web. [D] New technology.

　　24. [A] High bandwidth Internet connections

　　[B] Cable.

　　[C] Related technologies.

　　[D] Electronic devices.

　　25. [A] Online business. [B] Some new products.

　　[C] Cable modems. [D] A new high-speed network.