C#

public CLIPSNet.DataTypes.Multifield h = new CLIPSNet.DataTypes.Multifield();

       private void Form1_Load(object sender, EventArgs e)
       {
           CLIPSNet.Environment j = new CLIPSNet.Environment();
           int i = j.Load(@"..\..\..\instance.clp");
           j.Reset();

int x;
List<int> lis = new List<int>();
Node<int> chou = lis.GetFirst();
x = int.Parse(Console.ReadLine());
lis.GetFirst().SetInfo(x);
while (chou.GetInfo() != -1)
{
    x = int.Parse(Console.ReadLine());
    chou.SetInfo(x);
    chou = chou.GetNext();
}

using System;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
using System.Text;

namespace scratchpad3
{
    class Program
    {
        public static void Main()
        {
            var dm = new DocumentManager<Document>(); //************************2
            dm.AddDocument(new Document("Title A", "Sample A"));//**************4
            dm.AddDocument(new Document("Title B", "Sample B"));
            dm.DisplayAllDocuments();
            if (dm.IsDocumentAvailable)
            {
                Document d = dm.GetDocument();
                Console.WriteLine(d.Content);
                Console.Read();
            }

        }
    }

//    >>>>>>>>>>>>>>>>>>>>>>>>> decl of a class
    public class DocumentManager<T>
where T : IDocument			//************************1
    {
        private readonly Queue<T> documentQueue = new Queue<T>();
        public void AddDocument(T doc) //************************3
        {
            lock (this)
            {
                documentQueue.Enqueue(doc);
            }
        }
        public bool IsDocumentAvailable
        {
            get { return documentQueue.Count > 0; }
        }

        public T GetDocument()
        {
            T doc = default(T);
            lock (this)
            {
                doc = documentQueue.Dequeue();
            }
            return doc;
        }
         public void DisplayAllDocuments()
        {
            foreach (T doc in documentQueue)
            {
                Console.WriteLine(doc.Title);
            }
        }



    }

//>>>>>>>>>>>>>>>>>>>>>>>>>>>>> decl of a class
    public interface IDocument
    {
        string Title { get; set; }
        string Content { get; set; }
    }
    public class Document : IDocument
    {
        public Document()
        {
        }
        public Document(string title, string content)
        {
            this.Title = title;
            this.Content = content;
        }
        public string Title { get; set; }
        public string Content { get; set; }       
    }
}

Q3) Let us take a view of this part of the coding:-

 public void AddDocument(T doc) // //************************3
"T  doc" may create a reference variable to an object called doc
but instead of passing a reference variable we are passing an object in the method call as:-

 dm.AddDocument(new Document("Title A", "Sample A"));//************************4
etc ....
case1)  Why this anomaly?
Case2)   Can we intuitively know from a coding where it is a reference variable that is to be passed as a paremeter and where an object is to be passed as a parameter?