using System;
 
public class Test
{
	public static void Main()
	{
		// your code goes here
	}
}
 
  namespace A
  {
 
     public abstract class BaseClass
     {
         protected virtual string GetData()
         {
             throw new NotImplementedException();
         }
     }
  }
 
  namespace B  //includes a reference to A
  {
  	 public abstract class BaseClass
     {
     }
 
 
     abstract class DerivedClassA : BaseClass
     {
 
     }
 
 
     internal class DerivedClassB: DerivedClassA
     {
          public void write()
          {
             base.GetData(); // results in error.
 
             // The name 'GetData' does not exist in the current context
             // and DerivedClassA does not contain a definition for 'GetData'
          }
     }
  }

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