设有以下定义和程序:#include<iostream.h>class A1{public: void show1() { cout<<'class A1'<<endl; } }class A2 : public A1{public: void show2() { cout<<'class A2'<<end1 }}class A3 : protected A2{public: void show3() { cout<<'class A1'<<endl }}void main(){ A1 obj1 A2 obj2 A3 obj3} 则以下不合语法的调用语句是