„Winter Squash“. University of Illinois Extension. Qaraldi: 2013-yil 15-sentyabr.
oregonstate.edu
lpi.oregonstate.edu
„Vitamin A“. Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis (2016-yil 1-iyul). Qaraldi: 2021-yil 21-dekabr.