You are answering a USMLE-style medical question. Question: A 20-year-old woman presents with vaginal discharge, pruritus, and painful micturition for the past 5 days. She is sexually active with multiple partners and admits to using barrier protection inconsistently. Her last menstrual period was 2 weeks ago. The patient denies any fever, chills, abdominal pain, menorrhagia, or flank pain. She is afebrile and the vital signs are within normal limits. Speculum examination reveals vaginal erythema with a profuse, greenish-yellow, purulent, malodorous discharge. The vaginal pH is 5.5. Vaginal swab and urine samples are obtained for microscopy and culture, and results are pending. Which of the following is the most likely diagnosis in this patient based on her presentation? Options: A) Urinary tract infection B) Bacterial vaginosis C) Trichomonal vaginitis D) Chlamydia infection Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.