how to display drop down list item for a certain condition ?

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VB

hello and good day. i'm using vb.net

this is my drop down list:

<asp:DropDownList ID="ddl1" runat="server">
            <asp:ListItem Value=""></asp:ListItem>
            <asp:ListItem Value="1"></asp:ListItem>
            <asp:ListItem Value="2"></asp:ListItem>
            <asp:ListItem Value="3"></asp:ListItem>
            <asp:ListItem Value="4"></asp:ListItem>
            <asp:ListItem Value="5"></asp:ListItem>
            </asp:DropDownList>

I want to do something like this

if textbox1.text = "abc" Then

ddl1.selectedvalue = "1" = visible
ddl1.selectedvalue = "2" = visible
ddl1.selectedvalue = "3" = invisible
ddl1.selectedvalue = "4" = invisible
ddl1.selectedvalue = "5" = invisible

Thank you