You are answering a USMLE-style medical question. Question: A 33-year-old G2P1 woman presents to the office because of poor diabetic control. She is currently at 18 weeks gestation and admits to having poor control of her type 1 diabetes before becoming pregnant. Her family history is non-contributory. The physical examination shows a pregnant woman with a fundal height of 20 cm (7.9 in). An abdominal ultrasound is ordered. Which of the following is the most likely congenital abnormality shown on the ultrasound? Options: A) Amelia B) Sacral agenesis C) Spina bifida D) Ventricular septal defect Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.