XmlElement не находит узел C#

Пишу код читалку fb2 книг. Из списка данных о книге выводит только данные файла (вес, дату). Смотрел по отладке descriptionNode и bodyNode выдают Null. Подскажите в чем проблема?

    public Book ReadBook(string filePath)
    {
        Book book = new Book();

        XmlDocument doc = new XmlDocument();
        doc.Load(filePath);

        XmlElement root = doc.DocumentElement;
        if (root != null)
        {
            XmlNode descriptionNode = root.SelectSingleNode("description");
            if (descriptionNode != null)
            {
                Console.WriteLine("work =" + descriptionNode.InnerText);
                XmlNode titleInfoNode = descriptionNode.SelectSingleNode("title-info");
                if (titleInfoNode != null)
                {   
                    Console.WriteLine("work =" + titleInfoNode.InnerText);
                    book.Title = GetElementValue(titleInfoNode, "book-title");
                    book.Authors = GetAuthorName(titleInfoNode.SelectSingleNode("author"));
                    book.Genre = GetElementValue(titleInfoNode, "genre");
                    book.Language = GetElementValue(titleInfoNode, "lang");
                }
            }
            book.AddedDate = File.GetCreationTime(filePath);
            book.Size = GetFileSizeInMB(filePath);

            XmlNode bodyNode = root.SelectSingleNode("body");
            if (bodyNode != null)
            {
                book.Content = bodyNode.InnerXml;
            }
        }

        return book;
    }

    private string GetElementValue(XmlNode node, string elementName)
    {
        XmlNode element = node.SelectSingleNode(elementName);
        return element?.InnerText ?? string.Empty;
    }

    private string GetAuthorName(XmlNode authorNode)
    {
        if (authorNode == null)
            return string.Empty;

        string firstName = GetElementValue(authorNode, "first-name");
        string lastName = GetElementValue(authorNode, "last-name");

        return $"{lastName} {firstName}".Trim();
    }

    private double GetFileSizeInMB(string filePath)
    {
        FileInfo fileInfo = new FileInfo(filePath);
        return Math.Round(fileInfo.Length / 1048576.0, 2);
    }

UPD: У меня есть другая версия кода Linq2xml:

        public Book ReadBook(string filePath)
        {
            XDocument doc = XDocument.Load(filePath);
            Book book = new Book();
            book.Title = GetBookTitle(doc);
            book.Authors = GetBookAuthors(doc);
            book.Genre = GetBookGenre(doc);
            book.Language = GetBookLanguage(doc);
            book.AddedDate = File.GetCreationTime(filePath);
            book.Size = GetFileSizeInMB(filePath);
            book.Content = GetBookContent(doc);
            return book;
        }
        private string GetBookTitle(XDocument doc)
        {
            XElement titleElement = doc.Root?.Element("description")?.Element("title-info")?.Element("book-title");
            return titleElement?.Value ?? string.Empty;
        }
        private string GetBookAuthors(XDocument doc)
        {
            XElement authorElement = doc.Root?.Element("description")?.Element("title-info")?.Element("author")?.Element("first-name");
            string firstName = authorElement?.Value ?? string.Empty;
            authorElement = doc.Root?.Element("description")?.Element("title-info")?.Element("author")?.Element("last-name");
            string lastName = authorElement?.Value ?? string.Empty;
            //foreach
            return $"{lastName} {firstName}".Trim();
        }
        private string GetBookGenre(XDocument doc)
        {
            XElement genreElement = doc.Root?.Element("description")?.Element("title-info")?.Element("genre");
            //foreach
            return genreElement?.Value ?? string.Empty;
        }
        private string GetBookLanguage(XDocument doc)
        {
            XElement langElement = doc.Root?.Element("description")?.Element("title-info")?.Element("lang");
            return langElement?.Value ?? string.Empty;
        }
        private string GetBookContent(XDocument doc)
        {
            XElement bodyElement = doc.Root?.Element("body");
            return bodyElement?.Value ?? string.Empty;
        }
        private double GetFileSizeInMB(string filePath)
        {
            FileInfo fileInfo = new FileInfo(filePath);
            return Math.Round(fileInfo.Length / 1048576.0, 2);
        }