StreamReader stream = new StreamReader("Online.xml");
            XmlTextReader reader = null;
            reader = new XmlTextReader(stream);
            while (reader.Read())
            {
                switch (reader.NodeType)
                {
                    case XmlNodeType.Element:
                        break;
                    case XmlNodeType.Text:
                        Console.Write(reader.Value + " ");
                        break;
                    case XmlNodeType.EndElement:
                        break;
                }
            }

<a>a1</a>
<b>b1</b>
<c>c1</c>
<d>d1</d>
<a>a2</a>
<b>b2</b>
<c>c2</c>
<d>d2</d>
<a>a3</a>
<b>b3</b>
<c>c3</c>
<d>d3</d>

There are multiple root elements. Line 2, position 2.