Oprea, E., & Underwood, C. (2016). The 4 x 4 diet: 4 key foods, 4-minute workouts, four weeks to the body you want (First edition.). Harmony Books.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Oprea, Erin, و Carrie Underwood. The 4 X 4 Diet: 4 Key Foods, 4-minute Workouts, Four Weeks to the Body You Want. First edition. New York: Harmony Books, 2016.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Oprea, Erin, و Carrie Underwood. The 4 X 4 Diet: 4 Key Foods, 4-minute Workouts, Four Weeks to the Body You Want. First edition. Harmony Books, 2016.
تحذير: قد لا تكون هذه الاستشهادات دائما دقيقة بنسبة 100%.