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Dyfyniad Arddull ChicagoWilliams, John Whitridge, F. Gary Cunningham, Paul C. MacDonald, Norman F. Gant, and John Whitridge Williams. Williams Obstetrics. Norwalk, CT: Appleton & Lange, 1989.
Dyfyniad MLAWilliams, John Whitridge, et al. Williams Obstetrics. Appleton & Lange, 1989.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.