单项选择题

有如下程序 #include <iostream> using namespace std; class Base { protected: Base( ){cout<<’A’; } Base(char c) { cout<<c; } }; class Derived: public Base { public: Derived(char c){ cout<<c; } }; int main( ){ Derived d1 (’B’); return 0; } 执行这个程序屏幕上将显示输出

A.B
B.BA
C.AB
D.BB