I am using VB. How to select mult iteams in listbox using backend code?

[Link_1]

I am using VB. How to select mult iteams in listbox using backend code?

I have a listbox where user can select muti items.

    <asp:ListBox ID="lb" SelectionMode="multiple" runat="server"  DataValueField="dv">
        <asp:ListItem>red r</asp:ListItem>
        <asp:ListItem>blue b</asp:ListItem>
        <asp:ListItem>green g</asp:ListItem>
    </asp:ListBox>

How can I set so the value of "blue b" and "green g" is already selected? I tried setSelected but this method is not supported.

lb.SetSelected(1, True)
lb.SetSelected(2, True)

I also tried this below which kind of works. It does select 1 value but I need to able to select multi values.

lb.Text = "blue b"
lb.Text = "green g"

I tried this also and it doesn't select any values.

lb.Text = "blue b green g"