Olson, S. F. (1998). Open horizons (1st University of Minnesota ed.). University of Minnesota Press.
Dyfyniad Arddull ChicagoOlson, Sigurd F. Open Horizons. 1st University of Minnesota ed. Minneapolis: University of Minnesota Press, 1998.
Dyfyniad MLAOlson, Sigurd F. Open Horizons. 1st University of Minnesota ed. University of Minnesota Press, 1998.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.