听下面一段独白 , 回答第 17 至第 20 四个小题。 17. When will the exhibition end? A. On October3rd. B. On October7th. C. On October9th. 18. Why is the whole exhibition are a flooded with water? A. To make visitors concern about rising sea levels. B. To show how the ice is disappearing. C. To try to make fun for visitors. 19. What can you see on the walls of the exhibition hall? A. Photos of the scenery of the Arctic. B. Posters about global warming. C. Introductions to the exhibition. 20. What are people encouraged to do on computers? A. Search for information. B. Ask scientists questions. C. E-mail their friends.