有下列程序: #include<iosteram.h> using namespace std; class Base { public: Base(){cout<< BB ; f(); } void f(){cout<< Bf ;} }; class Derived:public Base { public: Derived(){cout<< DD ;} void f(){cout<< Dff;} }; int main(){Derived d;return 0;} 执行上面的程序将输出( )。
A.BBBfDD
B.BBDfDDDf
C.DD
D.DDBBBf