Which C++ inheritance access specifier, when used to inherit a base class, causes all public and protected members of the base class to become private members of the derived class?

With private inheritance, both the public and protected members of the base class become private members of the derived class, meaning they are accessible within the derived class itself but are no longer accessible to any further classes that might inherit from the derived class, nor to outside code through a derived-class object. Public inheritance (option A) preserves the original access levels ('is-a' relationship). Protected inheritance (option B) downgrades public members specifically to protected, while protected members remain protected. There is no such thing as 'friend inheritance' as an inheritance access specifier (option C); friendship is a separate, unrelated C++ mechanism. Virtual inheritance (option D) addresses the diamond inheritance problem and is unrelated to access-level downgrading.