APA Style
National Geographic Vol. 199 No. 4, April 2001. (2001).
Washington:
National Geographie.
Chicago Style
National Geographic Vol. 199 No. 4, April 2001.
.
Washington:
National Geographie,
2001.
.
MLA Style
National Geographic Vol. 199 No. 4, April 2001.
.
Washington:
National Geographie,
2001.
.
Turabian Style
National Geographic Vol. 199 No. 4, April 2001.
Washington:
National Geographie,
2001.
.