Подскажите как исправить ошибку

using System;
 
 
namespace Project{
 
    class MyApplication{
      public static void Main(String[] args){
        string README = "This program has created NIKITA";
 
        RobotsFeatures b2 = new RobotsFeatures(300,"black","B2");
        b2.OutputFeatures();
        RobotsFeatures b3 = new RobotsFeatures(200,"white","B3");
        b3.OutputFeatures();
        BotsFeatures b4 = new BotsFeatures(200,"white","B3");
        b4.OutputFeatures();
        
 
 
 
 
        using(FileStream stream = new FileStream("README.txt",FileMode.OpenOrCreate)){
            byte[] array = System.Text.Encoding.Default.GetBytes(README);
            stream.Write(array, 0 , array.Length);
        }
        
          
      }
       
    }
    
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections.Generic;
using System.IO;
 
namespace Project{
    class RobotsFeatures{
        public static int speed; 
        public static string ?color,name;
    
    public RobotsFeatures(int speed, string color, string name){
        System.Console.WriteLine("Robot has created");
        GetFeatures(speed,color,name);
    }
 
    public void GetFeatures(int speed, string color, string name){
        RobotsFeatures.speed = speed;
        RobotsFeatures.color = color;
        RobotsFeatures.name = name;
    }
    public void OutputFeatures(){
        System.Console.WriteLine(name + " " + color + " have speed = " + speed);
    }
 
 
 
 
    }
    
}

using System;
 
namespace Project{
 
    class BotsFeatures : RobotsFeatures{
        
    }
}

    class BotsFeatures : RobotsFeatures{
        public BotsFeatures(int speed, string color, string name) : base(speed, color, name) {}
    }