给定关系模式R（U，F），其中：U为关系模式R中的属性集，F是U上的一组函数依赖。假设U={A1，A2，A3，A4}，F={A1→A2，A1A2→A3，A1→A4，A2→A4}，那么关系R的主键应为（ ）。函数依赖集F中的（ ）是冗余的。
问题1选项
A.A1
B.A1A2
C.A1A3
D.A1A2A3
问题2选项
A.A1→A2
B.A1A2→A3
C.A1→A4
D.A2→A4
正确答案及解析
正确答案
解析
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