Disable multiple items from DropDownList. Someone need to check code!

Hello,
I would like to disable a specific items from DropDownList. I have below code but it does not working. So, need someone to told me what I'm doing wrong. DropDownList have 5 items.
And, I'm getting error:
Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index

Protected Sub CheckBox1_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles CheckBox1.CheckedChanged
        Dim X As Integer = 0 <> 1
        DropDownList1.Items(X).Enabled = False

    End Sub

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But, if I add a different value for X, then it disable 1st and 2nd item.

Protected Sub CheckBox1_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles CheckBox1.CheckedChanged
        Dim X As Integer = 0 or 1
        DropDownList1.Items(X).Enabled = False

    End Sub

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My goal is if I would have a 365 items in DropwDownList to disable items for example between 120 and 150.

Thank you in advance for help to anyone.