【正确答案】 A

【答案解析】原文：W: Mr. Smith, what’s wrong with your smartphone?M: It wouldn’t give sound when phone calls come in.W: Have you checked its sound system?M: Yes, the sound system is OK.W: When did you buy the smartphone?M: Three days ago.W: In that case, you can return it to us or change it for a new one.M: I want to change it for a new one.W: OK. Have you brought the receipt with you?M: Yes, here you are.17. What has happened to the man’s smartphone?18. When did the man buy the smartphone?19. What does the woman ask the man to show?信息明示题。对话中，女士询问男士什么时间购买的这部智能手机，男士回答说三天前。由此可见，男士购买这部智能手机的时间是三天前，所以本题的答案为A)“三天前”。B)“六天前”、C)“一个月以前”和D)“三个月以前”均与对话内容不符，因此可以排除。