下列代码段的运行结果为（ ）。
public class Test {
public static void main (String[] args){
int a = 30;
int b = 20;
int tmp = a;
a = b;
b = tmp;
System.out.println(a+","+b);
}
}
A.30,20 B.20,20
C.30,30 D.20,30