Dyfyniad APA
Verschuur, G. L. (1996). Impact!: The threat of comets and asteroids. Oxford University Press.
Dyfyniad Arddull Chicago
Verschuur, Gerrit L. Impact!: The Threat of Comets and Asteroids. New York: Oxford University Press, 1996.
Dyfyniad MLA
Verschuur, Gerrit L. Impact!: The Threat of Comets and Asteroids. Oxford University Press, 1996.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.