Concatenation using LINQ

 using System;  
 using System.Collections.Generic;  
 using System.Linq;  
 using System.Text;  
 using System.Linq.Expressions;  
 namespace ConsoleApplication1  
 {  
   public class Student  
   {  
     public string FirstName;  
     public string LastName;  
   }  
   class Program  
   {  
     static void Main(string[] args)  
     {  
       Student s1 = new Student { FirstName = "Jack", LastName = "Frost" };  
       Student s2 = new Student { FirstName = "Mary", LastName = "Wong" };  
       Student s3 = new Student { FirstName = "Ronald", LastName = "McDonalds" };  
       Student s4 = new Student { FirstName = "John", LastName = "Smith" };  
       List<Student> studentArray = new List<Student>() { s1, s2, s3, s4 };  
       string nameList = studentArray.OrderBy(m => m.LastName).Select(m => m.LastName).Aggregate((current, next) => current + ", " + next);  
       Console.WriteLine(nameList);  
       Console.ReadLine();  
     }  
   }  
 }