A 64-Year-Old Woman Gravida 2, Para 2, Comes to the Physician

A 64-year-old woman gravida 2, para 2, comes to the physician because of fatigue and an increase in abdominal girth despite a 5-kg (11.0-lb) weight loss over the past 6 months. She takes no medications and has received all recommended vaccinations. BMI is 30kg/m².  Abdominal examination shows shifting dullness. There is tenderness to palpation of the left lower quadrant but no guarding or rebound. Bimanual palpation shows a small uterus and a left adnexal mass. Her blood work shows a marked elevation of CA-125.  Which of the following most likely would have reduced the risk of this patient's condition?

A) Consistent condom use
B) Long-term antioxidant supplementation
C) Nulliparity
D) Use of oral contraceptives
E) Vaccination