using System;

using System.Windows.Forms;

namespace Demo

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

            webBrowser1.DocumentText = ("<select id=\"pid\" onchange=\"gradeChange()\">" +

                                        "<option grade=\"1\" value=\"a\">选项一</a>" +

                                        "<option grade=\"2\" value=\"b\">选项二</a>" +

                                        "</select>" +

                                        "<script type=\"text/javascript\">" +

                                        "function gradeChange(){" +

                                        "var objS = document.getElementById(\"pid\");" +

                                        "var grade = objS.options[objS.selectedIndex].grade;" +

                                        "alert(grade);" +

                                        "}" +

                                        "</script>");

        }

        private void button2_Click(object sender, EventArgs e)

        {

            HtmlElementCollection elements = webBrowser1.Document.GetElementById("pid").GetElementsByTagName("option");

            foreach (HtmlElement option in elements)

            {

                option.SetAttribute("selected", "selected");

                webBrowser1.Document.GetElementById("pid").RaiseEvent("onchange");

                break;

            }

        }

    }

}