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
To diagnose well being of fetus. most reliable method : 
Select and explain. 
A. L:S ratio, B. HPL levels, C. Kick test, D. Ultrasound
D: Ultrasound
Answer: D: Ultrasound 
Explanation: Ultrasound