使用mshtml不起作用

我有一个c#应用程序，我尝试使用一些mshtml元素。但我有个问题。using mshtml;命名空间给我一个错误是Visual Studio 2012。

这是我的源代码，

namespace Tagger
{
    using mshtml;
    using System;
    using System.Collections;
    using System.Collections.Generic;
    using System.Runtime.CompilerServices;
    using System.Text;
    public class HTMLForm
    {
        private string _action = "";
        private string _method = "";
        public Hashtable Inputs = new Hashtable();
        public HTMLForm(IHTMLFormElement element)
        {
            this._method = element.method;
            this._action = element.action;
            foreach (IHTMLInputElement element2 in (IHTMLElementCollection) element.tags("input"))
            {
                try
                {
                    string name = element2.name;
                    string str2 = element2.value;
                    if (name == null)
                    {
                        name = element2.type;
                    }
                    this.Inputs.Add(name, str2);
                }
                catch
                {
                }
            }
        }
        public static HTMLForm[] GetAllForms(string html)
        {
            List<HTMLForm> list = new List<HTMLForm>();
            HTMLDocument document = (HTMLDocument) Activator.CreateInstance(Type.GetTypeFromCLSID(new Guid("25336920-03F9-11CF-8FD0-00AA00686F13")));
            document.write(new object[] { html });
            document.close();
            foreach (IHTMLFormElement element in document.forms)
            {
                list.Add(new HTMLForm(element));
            }
            return list.ToArray();
        }
        public static HTMLForm GetFormByAction(string html, string action)
        {
            foreach (HTMLForm form in GetAllForms(html))
            {
                if (form.Action.ToLower() == action.ToLower())
                {
                    return form;
                }
            }
            return null;
        }
        public string ToPostData()
        {
            StringBuilder builder = new StringBuilder();
            foreach (string str in this.Inputs.Keys)
            {
                object obj2 = this.Inputs[str];
                string str2 = (obj2 == null) ? "" : obj2.ToString();
                builder.AppendFormat("{0}={1}&", HTTPBase.encode(str), HTTPBase.encode(str2));
            }
            if (builder.Length > 1)
            {
                return builder.ToString().Substring(0, builder.Length - 1);
            }
            return "";
        }
        public string Action
        {
            get
            {
                return this._action;
            }
            set
            {
                this._action = value;
            }
        }
        public string Method
        {
            get
            {
                return this._method;
            }
            set
            {
                this._method = value;
            }
        }        
    }
}

但是我不能使用htmlelement, IHTMLElementCollection的函数。编译器给了我一个错误。

错误1无法找到类型或命名空间名称'mshtml'您缺少using指令或程序集引用吗?)

Error 5   The type or namespace name 'HTMLDocument' could not be found (are 

您缺少using指令或程序集引用?

错误2无法找到类型或命名空间名称'IHTMLFormElement'缺少using指令或程序集引用?)

错误3类型或命名空间名称'IHTMLElementCollection'无法找到(您是否缺少using指令或程序集引用?)

错误4类型或命名空间名称'HTMLDocument'找不到(您是否缺少using指令或程序集引用?)