怎么判断checkbox是否被选中？

  protected void btnOK_Click(object sender, EventArgs e)    {        System.Collections.Specialized.NameValueCollection nc = new System.Collections.Specialized.NameValueCollection(Request.Form);        System.Web.UI.HtmlControls.HtmlInputCheckBox ck;        string cc="";        for (int i = 0; i < rpt310GuessAdd.Items.Count; i++)        {             cc = nc.GetValues("SMONEY")[i].ToString();            //            //这里怎么获取ck是否被选中            ck=(HtmlInputCheckBox)------这一句怎么写？？            if (ck.Checked)            {                 ck.Disabled = false;            }                 }          }