A:有极大值2,极小值﹣2
B:有极大值﹣2,极小值2
C:无极大值,但有极小值﹣2
D:有极大值2,无极小值
读北京图,回答下列问题.
He has ordered a watch on line for his father and it _______ to him before Father's Day.
能证明锌、铜、银的金属活动性顺序的一组试剂是 ( )①铜、银、硝酸锌溶液;②锌、银、硝酸铜溶液;③锌、铜、稀硫酸、硝酸银溶液;④锌、铜、稀硫酸。