听力原文:W: Good afternoon, Uncle Smith. M: Good afternoon, Cathy. W: There will be a dinner party for my birthday. Would you come? M: I'd love to. When? W: Next Saturday. M: I'm afraid I'm busy then. I have to meet a foreign friend at the airport. W: That's OK. What about Sunday? M: That will be all right. W: That's great. You can come at around 7:00 and we can chat for a while before the party starts. Why did Cathy invite Uncle Smith to dinner?