Класс "Студент" и "Студенческая группа" - C#

using System;
using System.Collections.Generic;
using System.Linq;
 
namespace CyberF
{
    class Student
    {
        public string Card;
        public string FirstName;
        public string LastName;
        public string MiddleName;
        public DateTime BirthDay;
        public int[] Evaluations = new int[5];
 
        public Student(string card, string firstName, string lastName, string middleName, DateTime birthDay, int[] evaluations)
        {
            Card = card;
            FirstName = firstName;
            LastName = lastName;
            MiddleName = middleName;
            BirthDay = birthDay;
            Evaluations = evaluations;
        }
 
        public double GetAverageScore() => Evaluations.Average();
 
        public override string ToString()
        {
            return $"#{Card} {LastName} {FirstName.Substring(0, 1)}. {MiddleName.Substring(0, 1)}. [Average score: {GetAverageScore():N2}]";
        }
    }
 
    class StudentGroup
    {
        List<Student> _students = new List<Student>();
        public string Name;
        public string Course;
        
        public StudentGroup(string name, string course, List<Student> students)
        {
            Name = name;
            Course = course;
            _students.AddRange(students);
        }
 
        public double GetAverageScore()
        {
            return _students.Average(x => x.GetAverageScore());
        }
 
        public IEnumerable<string> SortByLastName()
        {
            foreach (var item in _students.OrderBy(x => x.LastName))
            {
                yield return item.ToString();
            }
        }
 
        public override string ToString()
        {
            return $"Group: {Name}, course {Course}. Number of students: {_students.Count}";
        }
    }
 
    class Program
    {
        static void Main(string[] args)
        {
            List<Student> students = new List<Student>()
            {
                new Student("1", "Alexey", "Frolov", "Igorevich", new DateTime(1990, 11, 2), new int[] { 3, 4, 4, 5, 3}),
                new Student("2", "Sergey", "Semenov", "Alexeevich", new DateTime(1992, 1, 12), new int[] { 4, 3, 3, 3, 4}),
                new Student("3", "Andrey", "Volkov", "Konstantinovich", new DateTime(1993, 10, 6), new int[] { 3, 5, 4, 4, 3}),
                new Student("4", "Ilya", "Ivanov", "Igorevich", new DateTime(1991, 8, 19), new int[] { 3, 4, 4, 5, 4}),
                new Student("5", "Arseniy", "Kot", "Arkadievich", new DateTime(1990, 6, 22), new int[] { 4, 5, 4, 3, 4}),
                new Student("6", "Pavel", "Fedorov", "Dmitrievich", new DateTime(1992, 5, 11), new int[] { 3, 5, 4, 5, 5})
            };
 
            Console.WriteLine("Students without sorting:");
            foreach (var student in students)
            {
                Console.WriteLine(student);
            }
 
            StudentGroup group = new StudentGroup("CyberF", "1", students);
 
            Console.WriteLine($"\n{group}" +
                $"\nAverage score of the group: {group.GetAverageScore():N2}.");
 
            Console.WriteLine("\nSorted students by lastname:");
            foreach (var student in group.SortByLastName())
            {
                Console.WriteLine(student);
            }
        }
    }
}