设有以下定义和程序： #include＜iostream.h＞ class A1 public: void show1() cout＜＜ class A1 ＜＜end1; ; class A2:public A1 public: void show2() cout＜＜ class A2 ＜＜end1; ; class A3:protected A2 public: void show3() cout＜＜ class A1 ＜＜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();