How do you implement polymorphism when defining a data relationship field type during data modelling?

How do you implement polymorphism when defining a data relationship field type during data modelling?
A . Map a field type to a concrete class at design-time and allow its actual type to be determined at run-time.
B . Map a field type to a class at design-time and allow its actual type to be determined by Pattern inheritance at run-time
C . Map a field type to a class at design-time and allow its actual type to be determined by Direct inheritance at runtime.
D . Map a field type to a class at design-time and allow its actual type to be determined by Direct inheritance at runtime.

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Answer: D