单项选择题

设个体域A={a,b},公式∀xP(x)∧彐xS(x)对在A上消去量词后应为()

A.P(x)∧S(x)
B.P(a)∧P(b)∧(S(a)∨S(b))
C.P(a)∧S(b)
D.P(a)∧P(b)∧S(a)∨S(b)