单项选择题

class TestReference{  
public static void main(String[] args){  
int x=2;  
TestReference tr = new TestReference();  
System.out.print(x);  
tr.change(x);  
System.out.print(x);  }  
public void change(int num){  
num = num + 1;  }  }  
程序运行后的输出是哪项()?  

A. 23
B. 21
C. 22
D. 编译错误

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