下列类ABC中所定义的构造函数，错误的是（）。

A. class ABC { private: int x, y; public: ABC() { x = 0; y = 0; } ABC(int a, int b) { x = a; y = b; } };
B. class ABC { private: int x, y; public: ABC() { x = 0; y = 0; } ABC(int a, int b); }; ABC::ABC(int a, int b) { x = a; y = b; }
C. class ABC { private: int x, y; public: ABC(int a = 0, int b = 0); }; ABC::ABC(int a, int b) { x = a; y = b; }
D. class ABC { private: int x = 0, y = 0; public: void Abc(int a, int b) { x = a; y = b; } };