Which of these is a valid Skolem form for ∀x∃yP(x,y)\forall x \exists y P(x, y)∀x∃yP(x,y)?
∀xP(x,f(x))\forall x P(x, f(x))∀xP(x,f(x))
∃yP(c,y)\exists y P(c, y)∃yP(c,y)
∀x∀yP(x,y)\forall x \forall y P(x, y)∀x∀yP(x,y)
∃xP(x,f(x))\exists x P(x, f(x))∃xP(x,f(x))