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