Show Hide ASP.Net TextBox based on DropDownList value in C#

How to make textbox true and false based on DropDownList_Changed more than one values

<asp:DropDownList ID="txt_typ_of_prcrmnt_in_cs_of_deptt_prchs" runat="server" CssClass="auto-style69"  ValidationGroup="First"
    AutoPostBack="true" OnSelectedIndexChanged="DropDownList_Changed"  Height="25px" Width="299px">
    <asp:ListItem Text="--Select Procurement type--" Value="C" />
    <asp:ListItem Text="Store" Value="Store" />
    <asp:ListItem Text="Gem" Value="Gem" />
    <asp:ListItem Text="Imprest site" Value="Imprest site" />
    <asp:ListItem Text="Cash" Value="Cash" />
    <asp:ListItem Text="From_site" Value="From_site" />
</asp:DropDownList>

protected void DropDownList_Changed(object sender, EventArgs e)
{
    DropDownList dropDownList = sender as DropDownList;
 
    if (txt_typ_of_prcrmnt_in_cs_of_deptt_prchs.SelectedItem.Value == "Store")
    {
        txt_dprtmntl_rg_s_no_page_n.Visible = false;
        txt_vndr_nm.Visible = false;
        txt_Vndr_mob_no.Visible = false;
        txt_amt.Visible = false;
        txt_purchs_by.Visible = false;
        txt_dt_of_prchs.Visible = false;
        // txt_rmk_one.Visible = false;
        Label7.Visible = false;
        Label8.Visible = false;
        Label9.Visible = false;
        Label10.Visible = false;
        Label11.Visible = false;
        Label12.Visible = false;
        RequiredFieldValidator5.Visible = false;
        RequiredFieldValidator6.Visible = false;
        RequiredFieldValidator7.Visible = false;
        RequiredFieldValidator8.Visible = false;
        RequiredFieldValidator9.Visible = false;
        RequiredFieldValidator10.Visible = false;
        RequiredFieldValidator11.Visible = false;
          
    }
     
    else
    {
        txt_dprtmntl_rg_s_no_page_n.Visible = true;
        txt_vndr_nm.Visible = true;
        txt_Vndr_mob_no.Visible = true;
        txt_amt.Visible = true;
        txt_purchs_by.Visible = true;
        txt_dt_of_prchs.Visible = true;
        // txt_rmk_one.Visible = true;
        Label7.Visible = true;
        Label8.Visible = true;
        Label9.Visible = true;
        Label10.Visible = true;
        Label11.Visible = true;
        Label12.Visible = true;
        RequiredFieldValidator5.Visible = true;
        RequiredFieldValidator6.Visible = true;
        RequiredFieldValidator7.Visible = true;
        RequiredFieldValidator8.Visible = true;
        RequiredFieldValidator9.Visible = true;
        RequiredFieldValidator10.Visible = true;
        RequiredFieldValidator11.Visible = true;
         
    }
 
 
    if (txt_typ_of_prcrmnt_in_cs_of_deptt_prchs.SelectedItem.Value == "From_site")
    {
        txt_dprtmntl_rg_s_no_page_n.Visible = false;
        txt_vndr_nm.Visible = false;
        txt_Vndr_mob_no.Visible = false;
        txt_amt.Visible = false;
        txt_purchs_by.Visible = false;
        txt_dt_of_prchs.Visible = false;
        // txt_rmk_one.Visible = false;
        Label7.Visible = false;
        Label8.Visible = false;
        Label9.Visible = false;
        Label10.Visible = false;
        Label11.Visible = false;
        Label12.Visible = false;
        RequiredFieldValidator5.Visible = false;
        RequiredFieldValidator6.Visible = false;
        RequiredFieldValidator7.Visible = false;
        RequiredFieldValidator8.Visible = false;
        RequiredFieldValidator9.Visible = false;
        RequiredFieldValidator10.Visible = false;
        RequiredFieldValidator11.Visible = false;
    }
 
    else
    {
        txt_dprtmntl_rg_s_no_page_n.Visible = true;
        txt_vndr_nm.Visible = true;
        txt_Vndr_mob_no.Visible = true;
        txt_amt.Visible = true;
        txt_purchs_by.Visible = true;
        txt_dt_of_prchs.Visible = true;
        // txt_rmk_one.Visible = true;
        Label7.Visible = true;
        Label8.Visible = true;
        Label9.Visible = true;
        Label10.Visible = true;
        Label11.Visible = true;
        Label12.Visible = true;
        RequiredFieldValidator5.Visible = true;
        RequiredFieldValidator6.Visible = true;
        RequiredFieldValidator7.Visible = true;
        RequiredFieldValidator8.Visible = true;
        RequiredFieldValidator9.Visible = true;
        RequiredFieldValidator10.Visible = true;
        RequiredFieldValidator11.Visible = true;
    }
}