Gaya APA

Sagan, C. (1997). Billion & Billions: Thoughts on Life and Death at the Brink of the Millenium (Cet 1). New York: The Ballantine Publishing Group.

Gaya MLA

Sagan, Carl. "Billion & Billions: Thoughts on Life and Death at the Brink of the Millenium". Cet 1 New York: The Ballantine Publishing Group, 1997. Text.