听力原文：W: Todays Arts Report features Dan Parker of the American Indian Dance Theatre. Mr Parker, I understand your troupe performs traditional music and dance from many different Native American cultures. Can you give us an idea of some of the dances youll be doing in your performance tonight? M: Certainly. Well be doing one thats a war dance. Originally it was a story-telling device to recount battles. Another is the grass dance performed by the Plains Indians, where they actually flatten tall field grass to prepare it for a ceremony. W: Since your dancers are from many different tribes, how can you be sure the dances are done correctly? M: Everything we do has been approved by the elders of our tribes. Thats partly because we dont necessarily know each others styles or dances. But its also because its hard to get complete agreement — even within the same tribe — about exactly how the dance should be done. W: Anyone who attends one of your performances will notice that your company goes to a lot of trouble to provide detailed explanations of the origin of the dances, the music, the costumes, and so forth. Could you explain to our listeners why you do this? M: Good question. There are always concerns that traditional dances performed in a theatre are nothing more than a spectacle. Our explanations show that in our cultures dance is custom rather than entertainment. We also want to make it clear to our audience that we are not performing any dances used for holy ceremonies. Questions 13 to 15 are based on the conversation you have just heard. 13. What is the main topic of the conversation? 14. What is the purpose of the interview? 15. Why are the dances approved by the elders of the tribes?13．