This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Study of fetal pas in first trimester with least radiation hazard : 
Select and explain. 
A. X-ray abdomen, B. Pelvimetry, C. CT scan, D. Ultrasound
D: Ultrasound
Answer: D: Ultrasound 
Explanation: Ultrasound