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: Radiology
The earliest sign of foetal life is best detected b: 
Select and explain. 
A. Doppler, B. Rcal time ultrasound, C. Fetoscopy, D. X-ray
B: Rcal time ultrasound
Answer: B: Rcal time ultrasound 
Explanation: Ans. Rcal time ultrasound