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选出正确的关系代数表达式。
查询所有“外科”病区和“内科”病区的所有医生姓名；

A.σName='外科'∨Name='内科'(π4(Q))
B.σName='外科'∧Name='内科'(π4(Q))
C.π4(σName='外科'∨Name='内科'(Q))
D.π4(σName='外科'∧Name='内科'(Q))

【参考答案】

C
C

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