Billings, E. 9 Metode Ovulasi Billings: Cara Alami Mengatur Kesuburan/ Cet.3. Kepustakaan Populer Gramedia.
Chicago Style (17th ed.) CitationBillings, Evelyn. 9 Metode Ovulasi Billings: Cara Alami Mengatur Kesuburan/ Cet.3. Kepustakaan Populer Gramedia.
MLA (8th ed.) CitationBillings, Evelyn. 9 Metode Ovulasi Billings: Cara Alami Mengatur Kesuburan/ Cet.3. Kepustakaan Populer Gramedia.
Warning: These citations may not always be 100% accurate.