serialize browsing number of URLs using webbrowser control

Question

I'm using webbrowser control... This is my code :

private void button1_Click(object sender, EventArgs e)
{
    foreach (string s in URLsList)
    {
        webBrowser1.Navigate(s);

    }

private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
  //Do something
}

but how can I serialize browsing of URLs and execute DocumentCompleted for each of them? How can I prevent from conflicts?