一道面试题

using System;
public class Test1
{
public static void Main()
{
int num = 0;
Person p = new Person("Li");
A1(p, num);
Console.WriteLine("{0},{1}", p.name, num);
}
static void A1(Person p, int num)
{
p = new Person("Wang");
num = 1;
}
}
public class Person
{
public string name;
public Person(string name)
{
this.name = name;
}
}

-------------------------------------------------------

using System;
public class Test1
{
public static void Main()
{
int num = 0;
Person p = new Person("Li");
A1(p, num);
Console.WriteLine("{0},{1}", p.name, num);
}
static void A1(Person p, int num)
{
p.name = "Wang";
num = 1;
}
}
public class Person
{
public string name;
public Person(string name)
{
this.name = name;
}
}

 两道题目的结果不同,求解释...