using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public class Student 

    {

        public int Id;

        public string StudentName;

    }

​

    public class Grade 

    {

        public int Id;

        public int StudentGrade;

    }

​

    public static void Main()

    {

            var students = new List<Student>{

            new Student{Id = 1, StudentName = "John"},

            new Student{Id = 2, StudentName = "Jane"},

            new Student{Id = 3, StudentName = "Joe"}

        };

        var grades = new List<Grade>{

            new Grade{Id = 1, StudentGrade = 5},

            new Grade{Id = 2, StudentGrade = 4},

            new Grade{Id = 3, StudentGrade = 6}

        };

        var studentGrades = students.Join(grades, s => s.Id, g => g.Id, (s, g) => new { s.StudentName, g.StudentGrade });

        foreach(var sg in studentGrades)

        {

            Console.WriteLine(sg.StudentName + ": " + sg.StudentGrade);

        }   

    }

}