This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: CVS Embryology, Subject name: Anatomy
Hea begins to beat in the week: 
Select and explain. 
A. 4, B. 5, C. 6, D. 7
A: 4
Answer: A: 4 
Explanation: Hea beat begins by day 22 post-ovulation and can be detected by Doppler ultrasound. It is week 4 post-ovulation (or feilization) and 6 weeks from LMP (Last Menstrual Period).