单项选择题

下面程序的运行结果为( )。 # include <iostream.h> class A { public: A( ) {cout <<"1";} ~A( ) {cout << "2";} }; class B:public A { public: B( ) {cout << "3";} ~B ( ) {cout << "4";} }; void main ( ) { B b; }

A.F10
B.F4
C.F5
D.Ctrl