Cita APA (7th ed.)
Blake, S., Serjeant, S., & Smith, S. Earth and Space. Open University.
Cita Chicago (17th ed.)
Blake, Stephen, Stephen Serjeant, i Sandy Smith. Earth and Space. Milton Keynes, Inglaterra: Open University.
Cita MLA (9th ed.)
Blake, Stephen, et al. Earth and Space. Open University.
Atenció: Aquestes cites poden no estar 100% correctes.