If universe of disclosure are all real numbers, then which of the following are true ? (A) ∃x ∀y (x + y…

All four statements are true over the real numbers. A holds with x = 0, since 0 + y = y for every y, and B holds because a non-negative x minus a negative y is always positive. C holds with x = 0 and y = −1, both non-positive, since 0 − (−1) = 1 > 0, and D holds because a product of reals is non-zero exactly when both factors are non-zero. Leaving out C wrongly assumes that two non-positive numbers cannot have a positive difference.