Abstract Class and Method in C#

using System;

namespace TestFile
{
    class Program
    {
        static void Main(string[] args)
        {

            Student UniStudent = new Student();
            Console.WriteLine("Student GPA is:" + UniStudent.ComputeGradeAverage());
            Console.WriteLine(UniStudent.OverallAcademicPerformance());
            
        }
    }


    public abstract class Person
    {
        public string firstName { set; get; }
        public string lastName { set; get; }
        public string emailAddress { set; get; }

        //Abstract Class Method
        public abstract float ComputeGradeAverage();
        //Non-Abstract Class Method
        public string OverallAcademicPerformance()
        {
            return "Good Academic Performance";
        }
    }

    public class Student : Person
    {
        public override float ComputeGradeAverage()
        {
            return 4.0f;
        }
    }
}