Option b is correct. A member of subtype is necessarily have to be a member of the supertype.
A parent type's attributes and capabilities are immediately carried through to its offspring. Additionally, the connection to inheritance is still present. Subtypes immediately inherit any changes made to these parent type's attributes or methods, and parent type changes likewise have an impact on subtypes.
Using object types in a type hierarchy, you may represent an entity, such as a customer, and describe various specific subtypes of customers under the original type. Each type is able to implement and carry out an operation in a different way once operations have been conducted on a hierarchy.
A subtype can be created from a supertype directly or indirectly, via higher levels of other subtypes. A supertype may have numerous sibling subtypes, whereas a subtype can only have one direct parent supertype (single inheritance).
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