“当时帝国地跨欧亚非三洲。境内农业、手工业和商业发展起来，海路畅通无阻，陆路纵横交错，四通八达，促进了贸易发展，也有利于信息传递和军队调动。帝国同北欧、印度、中国都有贸易往来，中国的丝绸也传入帝国。”

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    It's Sunday today. Sam and his friends are washing(洗)a car for Mr. Green. They can give the money from the car washing to their school football team. Mary and her friends are seeing a funny movie. They see an interesting cat in the movie. Ann is in the park with her mother. They're talking under a big tree. I think they are having a good time. Joan wants to know what her friend is doing. Her friend is in Japan, so Joan is writing a letter to her friend on her computer. May is cleaning the house with her parents. The family are very busy, but they're very happy. They are working and singing.

对Ag、Fe、Cu三种金属活动性顺序的探究，下列所选试剂不可行的是（　　）

“庄稼一支花，全靠肥当家”。合理使用化肥，才有利于农作物的生长和减少环境污染。下列有关化肥的说法正确的是(   )