translate the statement ? x? ? 0) ? (y ? 0)) ? (xy ? 0)) into english.
a) for every real number x and real number y, x or y are both nonnegative if and only if their product is nonnegative.
b) for every real number x and real number y, if x and y are both nonnegative, then their product is nonnegative.
c) for every real number x and real number y, x and y are both nonnegative if and only if their product is nonnegative.
d) for every real number x and real number y, if x or y are both nonnegative, then their product is positive.