题目

任务型阅读 （1） 根据对话内容，从方框内的选项中选出能填入的最佳选项，然后回答问题。 A. Are they my aunt's? B. The four keys are your father's.C. It's a key ring (钥匙环) with three keys.D. Can you help me find them?A：Hey, Frank. I need your help. B：What, Mom?A：Your aunt left (丢下) her keys in our house. B：Yes, Mom. Oh, four keys are on the sofa. A：No, they aren't. Your aunt only has three keys. B：I see. Oh, some keys are under the sofa, Mom.A：Let me have a look! Great! They're your aunt's. Thank you for your help, my dear son.设集合A⊆R，如果实数x0满足：对?r＞0，总?x∈A，使得0＜|x-x0|＜r，则称x0为集合A的聚点．给定下列四个集合：①Z；  ②{x∈R|x≠0}；   ③{nn+1|n∈Z，n≥0}；   ④{1n|n∈Z，n≠0}．上述四个集合中，以0为聚点的集合是（　　）A．①③B．②③C．①④D．②④