DropDownList collecting infos

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C#

ASP.NET

I have a problem that the dropdownlist just showing me one value even there is more than one like this one i have Gender (Male and Female).

DataTable tb1 = SQLHelper.Instance.getinfo("select GENDER_ID, GENDER_TYPE from gender");
        for (int i = 0; i < tb1.Rows.Count; i++)
        {
            string T = tb1.Rows[i][0].ToString();
            if (m == T)
                DropDownList1.Items.Add(new ListItem(tb1.Rows[i][1].ToString(), tb1.Rows[i][0].ToString(),true));
            else
                DropDownList1.Items.Add(new ListItem(tb1.Rows[i][1].ToString(), tb1.Rows[i][0].ToString(),false));
        }

Thanks In Advance