下列程序的输出结果是()。public class Test{static void operate(StringBuilder x, StringBuilder y){x.append(y);y = x;}public static void main(String[] args){StringBuilder a = new StringBuilder ("A");StringBuilder b = new StringBuilder ("B");operate(a,b);System.out.println(a+","+b);}}
A,B
B. AB,AB
C. AB,B
D. BB,AA