小明设计了下列四组物质，要求在一定条件下都能一步转化，其中错误的是（  ）

结合下列的概念图分析，叙述正确的是（   ）

    Many people like animals．Now a lot of people keep animals as pets(宠物)．Usually people like to keep dogs，cats，fish and other animals．Many young people keep animals because they think these animals are interesting．Some old people keep pets because they don’t live with their children．

    Martin lives in No．25 Garden Street．He is a doctor(医生)，but he helps dogs．People usually call him The Dog Doctor．When their dogs get sick(生病)，they call him on the telephone．He goes to the people’s houses and helps them．He gives the dogs the right medicine(药物)．Wherever(无论)he goes，he is always welcome．