...
using System.IO;
using System.ServiceModel.Syndication;
using System.Xml;
 
...
 
        private async void button2_Click(object sender, EventArgs e)
        {
            string url = "http://lenta.ru/rss";
 
            XmlReader reader = XmlReader.Create(url, new XmlReaderSettings() { Async = true });
 
            SyndicationFeed feed = SyndicationFeed.Load(reader);
 
            reader.Close();
            foreach (SyndicationItem item in feed.Items)
            {
                String subject = item.Title.Text;
                String summary = item.Summary.Text;
                ...
                MessageBox.Show(subject);
               
 
            }
        }