Express the negations of each of these statements so that all negation symbols immediately precede predicates.
a.∃z∀y∀xt (x, y, z)
b.∃x∃yp(x, y) ∧ ∀x∀yq(x, y)
c.∃x∃y(q(x, y) ↔ q(y, x))