单选题:有三个关系R、S和T如下: 由关系R和S通过运算得到关系T,则所使用的运算为(  )。

题目内容:
有三个关系R、S和T如下:


由关系R和S通过运算得到关系T,则所使用的运算为(  )。 A.笛卡尔积
B.交
C.并
D.自然连接

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