根据对话内容，选择恰当的句子补全下列对话。 A. Yes, but only once.                         B. I want to be a pop star. C. I want to be a movie star.                D. Can you play the guitar? E. Some day I'm going to make it. F. I'm going to buy an electric guitar when I have enough money. G. What are you going to buy when you have enough money? A: What do you like doing? B: Singing. 1___________ A: You can't be a famous pop star unless you're really good. 2__________ B: Yes. I always play my guitar when I listen to pop music on the radio. 3__________ A: Great! Have you been in any pop star competitions in your school? B: 4__________ I didn't win the prize. A: That's too bad! B: But it doesn't matter. I'll keep working hard. 5___________