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
True about intrauterine fetal death (IUD):a) Gas bubbles in great vesselsb) Halo's sign +vec) Overlapping of skull boned) Decreased amniotic fluid volume 
Select and explain. 
A. abc, B. ad, C. acd, D. bde
C: acd
Answer: C: acd 
Explanation: None