This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Surgery
Fetal cardiac activity can be detected by vaginal USG by howmany weeks after LMP 
Select and explain. 
A. 4 wks, B. 5 wks, C. 6 wks, D. 8 wks
C: 6 wks
Answer: C: 6 wks 
Explanation: Ans C Ref: Williams Obstetrics page 350First trimester evaluation With transvaginal scanningGestational sac reliably seen in uterus by 5 wksFetal echoes and cardiac activity by 6 wksCardiac motion typically observed when embryo is reached 5mm in length Sheila Balakrishnan-577Gestational sac - 4 1/2 wksYolk sac - 5wksFetal node - 5 1/2 wksFetal heart - 6wks