现有:  <br /> 1.  class Alpha { void m1() {} }  <br /> 2.  class Beta extends Alpha { void m2() { } }  <br /> 3.  class Gamma extends Beta { }  <br /> 4.  <br /> 5.  class GreekTest {  <br /> 6.    public static void main(String [] args) {  <br /> 7.      Alpha [] a = {new Alpha(), new Beta(), new Gamma() };  <br /> 8.      for(Alpha a2 : a) {  <br /> 9.        a2.m1();   <br /> 10.       if (a2 instanceof Beta || a2 instanceof Gamma)   <
A、A. a2.m2();
B、B. ((Beta)a2).m2();
C、C. ((Alpha)a2).m2();
D、D. ((Gamma)a2).m2();