Correct answer is (a) D∩T=Ø
For explanation I would say: Suppose P1 is a partially ordered class and a cut of P1 is pair (D, T) of nonempty subclasses of P1 satisfies the following properties: i) D∩T=Ø and D∪T=P1 ii) If z∈D and y≤z, then y∈D and iii) If z∈T and y≥z, then y∈T.