This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Carcinoma Ovary, Subject name: Gynaecology & Obstetrics
Protective factor for ovarian cancer: 
Select and explain. 
A. Nulliparity, B. Bilateral Tubectomy, C. Dysgenetic gonads, D. Woker of asbestos industry
B: Bilateral Tubectomy
Answer: B: Bilateral Tubectomy 
Explanation: Ans is b, i.e. Bilateral tubectomyRef: William gynae 3/ed, p736"Tubal ligation and Hysterectomy are each associated with a substantial reduction in risk. Theoretically, any gynecological procedure that precludes intants from reaching the ovaries via as caesarian from the lower genital tract might plausibly exert a similar protective effect." - Ref: Williams Gynae 3rd/ed, p736