[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.