Try this:

David Miller

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Private Sub Workbook_SheetActivate(ByVal Sh As Object)
If Sh.Name = "Trigger" Then
If Sheets("A").vibible = True And Sheets("B").Visible = True And
Sheets("C").Visible = True Then
Sheets("A").Visible = True
Sheets("B").Visible = True
Sheets("C").Visible = True
Else
Sheets("A").Visible = True
Sheets("B").Visible = True
Sheets("C").Visible = True
End If
End Sub