A、To have fun. B、To have a celebration. C、To welcome their guest. D、To welcome Cathy’s sister. B

A: Hello, Michael. How are things going?
B: Very well, thanks. Cathy, guess what, Tom and I have just won this year’s speech contest.
A: Oh, how wonderful! Congratulations!
B: Thanks. Are you free this Saturday evening? You see, we are thinking about having a Party,.... you know ... just to celebrate.
A: Yeah, I’ll be glad to come. You guys deserve to celebrate. You’ve been working so hard, haven’t you?
B: Yes, to tell the truth, we haven’t had a good night’s sleep last week. We need a break.
A: Are there any other people coming to the party?
B: We’ve invited some of our friends to come over and we would especially like you to join us.
A: I’d be delighted to. Thank you ... Um ... Would you like me to bring some food or drinks?
B: Oh, don’t bother. We’ve got everything ready.
A: Oh, that’s very kind of you. By the way, can I bring my sister to the party? She’s coming to visit me this weekend.
B: Sure, you can. She’ll be welcome.