C# Online Compiler | .NET Fiddle

using System;
using System.Text;
					
public class Program
{
	public abstract record Person(string FirstName, string LastName)
	{
		public sealed override string ToString()
		{
			StringBuilder stringBuilder = new StringBuilder();
			stringBuilder.Append("Base Record"); // type name
			stringBuilder.Append(" { ");
			if (PrintMembers(stringBuilder))
			{
				stringBuilder.Append(" ");
			}
			stringBuilder.Append("}");
			return stringBuilder.ToString();
		}
	
	}
	public record Teacher(string FirstName, string LastName, int Grade): Person(FirstName, LastName) 
	{
		
		public override string ToString()
		{
			StringBuilder stringBuilder = new StringBuilder();
			stringBuilder.Append("Teacher Record"); // type name
			stringBuilder.Append(" { ");
			if (PrintMembers(stringBuilder))
			{
				stringBuilder.Append(" ");
			}
			stringBuilder.Append("}");
			return stringBuilder.ToString();
		}
		
	}
	public record Student(string FirstName, string LastName, int Grade): Person(FirstName, LastName);
	
		
	
	public static void Main()
	{
		Person person1 = new Teacher("George", "Washington", 1);
		Console.WriteLine(person1);
	}
}

 
using System;
using System.Text;
                    
public class Program
{
    public abstract record Person(string FirstName, string LastName)
    {
        public sealed override string ToString()
        {
            StringBuilder stringBuilder = new StringBuilder();
            stringBuilder.Append("Base Record"); // type name
            stringBuilder.Append(" { ");
            if (PrintMembers(stringBuilder))
            {
                stringBuilder.Append(" ");
            }
            stringBuilder.Append("}");
            return stringBuilder.ToString();
        }
    
    }
    public record Teacher(string FirstName, string LastName, int Grade): Person(FirstName, LastName) 
    {
        

Compilation error (line 25, col 26): 'Program.Teacher.ToString()': cannot override inherited member 'Program.Person.ToString()' because it is sealed