Dyfyniad APA

Sagan, C. (1997). Billions and billions: Thoughts on life and death at the brink of the millennium. Headline Book Publishing.

Dyfyniad Arddull Chicago

Sagan, Carl. Billions and Billions: Thoughts on Life and Death at the Brink of the Millennium. London: Headline Book Publishing, 1997.

Dyfyniad MLA

Sagan, Carl. Billions and Billions: Thoughts on Life and Death at the Brink of the Millennium. Headline Book Publishing, 1997.

Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.