Final answer:
The correct declaration for a class named Book implementing a generic interface IRetainable should use angle brackets to specify the type, like this: public class Book : IRetainable. The options provided in the question are incorrect for declaring a generic interface in C#.
Step-by-step explanation:
The correct declaration for a public class named Book that implements a generic interface named IRetainable which works with the Book type is not listed among the given options. The syntax provided seems to resemble C# language, but none of the options are syntactically correct for declaring a generic interface implementation in C#. In C#, a generic interface is declared using angle brackets <>, and the type that the interface will operate on is specified within these brackets. An example of the correct declaration would be:
public class Book : IRetainable<Book>
This assumes that the IRetainable interface is designed to be generic. For instance, the declaration of the interface might look something like this:
public interface IRetainable<T>
Where T is a placeholder for the type parameter that will be provided by the implementing class, in this case, Book.