Multi-select from checkbox to form subreport?

[Lennon]

Well, I have a db of blood donors. And I making a vba query/filter to filter the donors with specific blood type (so A, B, AB or 0). I managed to get the filtered results for a or b or ab or 0, but i can't figured out how to filter result if I select two, three or all four blood types.

My code is:

In query:
Iif( Forms![Odabir]![KGr_A]; [KGr] ="A"; True)

And in vba:
Private Sub Odabir_M_Click()

Me.Odabir_Sub.Requery
Me.Odabir_Sub = Me.Odabir_Sub.ItemData(1)

End Sub