以下程序的执行结果是 【12 。#include ＜iostream.h＞class B{public:B(){}B(int i.int j);void printb();private:int a,b;};class A{public:A() { }A(int i,int j);void printa();private:B c;};A:: A(int i,int j):c(i, j){ }void A:: pfinta(){c. printb();}B::B(int i,int j){a=i;b=j;}void B::printb(){cout＜＜"a="＜＜a＜＜",b="＜＜b＜＜end1;}void main(){A m(7,9);m. printa();}