单选题 有如下程序：
#include＜iostream＞
using namespace std;
class Base
{
pubfic:
Base(){cout＜＜"BB";f();}
void f(){cout＜＜"Bf":}
};
class Derived:public Base
{
public:
Derived(){cout＜＜"DD";)
voidf(){cout＜＜"Df":}
};
intmain(){Derived d;retum 0;}
执行上面的程序将输出

• A.BBBfDD
• B.BBDfDDDf
• C.DD
• D.DDBBBf