Billings, E., & Westmore, A. (2007). Metode Ovulasi Billing. Cara Mengatur Kesuburan. KPG.
芝加哥风格引文Billings, Evelyn, 与 Ann Westmore. Metode Ovulasi Billing. Cara Mengatur Kesuburan. KPG, 2007.
MLA引文Billings, Evelyn, 与 Ann Westmore. Metode Ovulasi Billing. Cara Mengatur Kesuburan. KPG, 2007.
警告：这些引文格式不一定是100％准确.