与元组关系演算公式(?x)(P(x)∨Q(x))等价的是()

与元组关系演算公式(?x)(P(x)∨Q(x))等价的是()
A、(?x)(P(x)∧Q(x))
B、(┐?x)(┐P(x)∨┐Q(x))
C、(┐?x)(┐P(x)∧┐Q(x))
D、(?x)(┐P(x)∧┐Q(x))
【正确答案】：C

↑