Krisis | University of Groningen Press. Cambridge University Press.
Dyfyniad Arddull ChicagoKrisis | University of Groningen Press. Cambridge University Press.
Dyfyniad MLAKrisis | University of Groningen Press. Cambridge University Press.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.