You are answering a USMLE-style medical question. Question: A 79-year-old woman comes to the physician because of a 1-month history of difficulty starting urination and a vague sensation of fullness in the pelvis. Pelvic speculum examination in the lithotomy position shows a pink structure at the vaginal introitus that protrudes from the anterior vaginal wall when the patient is asked to cough. Which of the following is the most likely cause of this patient's symptoms? Options: A) Vaginal rhabdomyosarcoma B) Cystocele C) Rectocele D) Uterine leiomyomata Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.