How to retrieve data from two different tables and put it in to two different comboBox in C#?

I have two comboboxs(name and category) and two tables(tbl_participant and tbl_category). I want to retrieve data from tlb_paticipant to cboName and tbl_category to cboCategory when the form load. Below is the code for retrieve tbl_paticipant to cboName, but I don't know how to retrieve another one. Make tow connection, command, DataReader object?

        con = ConnectionDB.GetConnection();
        string sql = "select * from tbl_Participant";
        cmd = new SqlCommand(sql, con);

        try
        {
            con.Open();
            dr = cmd.ExecuteReader();
            while (dr.Read())
            {

                cboName.Items.Add(dr.GetValue(2).ToString());

            }
            cboName.SelectedIndex = 0;
            cmd.Dispose();
            con.Close();
        }
        catch (SqlException ex)
        {
            MessageBox.Show(ex.Message);
        }