Weldon, J., & Levitt, Z. (1975). UFO's: What on earth is happening? Harvest House Publishers.
Lua i Stíl Chicago (17ú heag.)Weldon, John, agus Zola Levitt. UFO's: What on Earth Is Happening? Irvine, Calif: Harvest House Publishers, 1975.
Lua MLA (9ú heag.)Weldon, John, agus Zola Levitt. UFO's: What on Earth Is Happening? Harvest House Publishers, 1975.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.