Problems 12-16 are based upon the following class declaration appearing in unknown.h All member functions will be defined in the file unknown.cpp class Unknown private: int a; public: Unknown (); // Initializes a to o void setA (const int aa); // Sets a equal to aa void GetA (int& aa) const; // Sends value of a to client through aa }; 12. Which of the following is a valid implementation for SetA ? A) void SetA(int aa) const B) void Unknown::SetA(aa) const C) void Unknown:: SetA() aa = a; a = aa; aa = a; D) void Unknown::SetA(const int aa) E) None of the answers provided a = aa; 13. Which of the following is a valid function heading for the function Unknown ? A) void Unknown(); D) int Unknown::Unknown() B) void Unknown::Unknown() E) None of the answers provided C) Unknown() 14. Which of the following is a valid function heading for the function GetA ? A) int Unknown::GetA(int& aa) D) int Unknown::GetA(int& aa) const B) void GetA(int& aa) E) None of the answers provided C) void Unknown::GetA(int& aa) const 15. Suppose that a client program has a variable X of type Unknown. Which of the following statements correctly outputs the current value of the private member a of the variable X? A) cout