有如下类声明: class XA { int x public: XA(int n){x=n} } class XB:public XA { int y; public: XB(int a,int b) } 在构造函数XB的下列定义中,正确的是
A.
XB::XB(int a,int b):x(a),y(b){}
B.
XB::XB(int a,int b):XA(a),y(b){}
C.
XB::XB(int a,int b):x(a),XB(b){}
D.
XB::XB(int a,int b):XA(a),XB(b){}