I'm trying to get some element from a <select> and <option> element.

This is my code:

for(int td = 1; td <= 1; td++)
{
    using (WebClient wc = new WebClient())
    {
        string pagina = wc.DownloadString("http://www.serebii.net/attackdex-xy/");
        HtmlDocument doc = new HtmlDocument();
        doc.LoadHtml(pagina);

        string attacco;
        //var prova = doc.DocumentNode.SelectSingleNode("/html/body/table[2]/tr[2]/td[2]/div[2]/table/tr/td[1]/form/select/option");

        foreach (HtmlNode node in doc.DocumentNode.SelectNodes(String.Format("/html/body/table[2]/tr[2]/td[2]/font/div[2]/table/tr/td[{0}]/select/option", td)))
        {
            attacco = node.NextSibling.InnerText;

            if(attacco != "AttackDex: A - G\n" && attacco != "AttackDex: H - R\n" && attacco != "AttackDex: S - Z\n")
            {
                var url = string.Format("http://www.serebii.net/attackdex-xy/{0}.shtml", attacco.ToLower().Replace(" ", ""));
                string attackPage = wc.DownloadString(url);
                HtmlDocument doc2 = new HtmlDocument();
                doc2.LoadHtml(attackPage);

                var category = doc.DocumentNode.SelectSingleNode("/html/body/table[2]/tr[2]/td[2]");
            }
        }
    }
}

And this is the code of html page:

<select name="SelectURL" onchange="document.location.href=document.nav.SelectURL.options[document.nav.SelectURL.selectedIndex].value" style="color:#383838; font-size: 8pt; background:#CEBC77" size="1">
 <option>AttackDex: A - G
</option><option value="/attackdex-xy/absorb.shtml">Absorb</option>
<option value="/attackdex-xy/acid.shtml">Acid</option>
<option value="/attackdex-xy/acidarmor.shtml">Acid Armor</option>
<option value="/attackdex-xy/acidspray.shtml">Acid Spray</option>
<option value="/attackdex-xy/acrobatics.shtml">Acrobatics</option>
<option value="/attackdex-xy/acupressure.shtml">Acupressure</option>
<option value="/attackdex-xy/aerialace.shtml">Aerial Ace</option>
<option value="/attackdex-xy/aeroblast.shtml">Aeroblast</option>
[...]

When I run the program the value of node (in foreach block) is NULL.