C # - How to put a secondary address in WebBrowser

Hello, How to put secondary address in WebBrowser in Visual Studio 2015.

        // webBrowser1
        // 
        resources.ApplyResources(this.webBrowser1, "webBrowser1");
        this.webBrowser1.Name = "webBrowser1";
        this.webBrowser1.ScriptErrorsSuppressed = true;
        this.webBrowser1.Url = new System.Uri("http://google.com.br", System.UriKind.Absolute);

If this address is unavailable, it will look for a secondary so that it does not return a browser error. (That we agree is very ugly)

Or simply check to see if this page is available. Otherwise, an error is returned by the MessageBox.