Interview Question asked on immutable

Interview Question asked to me in an interview.
What will be the output of the below program ?

 using System;   
  using System.Collections.Generic;   
  using System.Linq;  
 namespace LinqDetails  
 {  
   class Program  
   {  
     static void Main(string[] args)  
     {  
       DateTime dt = Convert.ToDateTime("9/2/2016");  
       dt.AddDays(1);  
       Console.WriteLine(dt);  
       Console.ReadLine();  
     }  
   }  
 }  

 Output

Because DateTime is immutable. :)