C# 中類別成員的預設存取權限是什麼？

using System;

namespace RectangleApplication {
   class Rectangle {
      //member variables
      private double length;
      private double width;

      public void Acceptdetails() {
         length = 10;
         width = 14;
      }

      public double GetArea() {
         return length * width;
      }

      public void Display() {
         Console.WriteLine("Length: {0}", length);
         Console.WriteLine("Width: {0}", width);
         Console.WriteLine("Area: {0}", GetArea());
      }
   }//end class Rectangle

   class ExecuteRectangle {
      static void Main(string[] args) {
         Rectangle r = new Rectangle();
         r.Acceptdetails();
         r.Display();
         Console.ReadLine();
      }
   }
}