Consider the following statements S1 and S2 about the relational data model: S1: A relation scheme can have at most one foreign key. S2: A foreign key in a relation scheme R cannot be used to refer to tuples of R. Which one of the following choices is correct?

Let us analyze both statements:

• Statement S1: A relation schema can have multiple foreign keys. For example, an Enrollment table can have foreign keys referencing both Student and Course tables. Thus, S1 is false.

• Statement S2: A foreign key in a relation $R$ can reference the primary key of the same relation $R$. This is known as a self-referencing relationship (e.g., an Employee relation having a ManagerID attribute that refers to the EmployeeID in the same Employee relation). Thus, S2 is false.

Hence, both S1 and S2 are false, which corresponds to option (D).