有如下程序: #include using namespace std; class Base{ public:virtual void Show(){cout<<’B’;} }; class Derived:public Base{ public:void Show(){cout<<’D’;} }; int main(){Base *p1=new Derived; Derived *p2=new Derived; p1->Show(); p2->Show(); delete p1; delete p2; return 0; }运行这个程序的输出结果是

A．BB

B．BD

C．DB

D．DD

铁的密度是7.9×10³kg/m³，它的物理意义是[ ]

A．1立方米的铁，密度是7.9×10³千克/米³

B．1立方米的铁，质量是7.9×10³千克/米³

C．1立方米的铁，密度是7.9×10³千克

D．1立方米的铁，质量是7.9×10³千克