Human blood types are determined by the presence or absence of three antigens: A, B, and Rh. Let $A$ be the set of people with the A antigen, $B$ be the set of people with the B antigen, and $R$ be the set of people with the Rh antigen (Rh-positive). A person with the blood type "O-negative" has none of these three antigens. Which set represents people with O-negative blood?