单项选择题
有如下程序: #inc1ude <iostream> using namespace std; c1ass Basel{ public: Basel(int d) {cout<<d;) ~Base1(){} }; c1ass Base2{ public: Base2(int d) {cout<<d;} ~Base2(){} }; c1ass Derived: public Basel, Base2{ public: Derived (int a,int b,int c,int d); Basel(b), Base2(a), bl(d), b2(c) {} Private: int b1; int b2; }; int main(){ Derived d(1,2,3,4); return 0; } 运行时的输出结果是( )。
A.1234
B.2134
C.12
D.21