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
The source of HCG is : 
Select and explain. 
A. Syncytiotrophoblast, B. Cytotrophoblast, C. Langhan's layer, D. Chorionic villi
A: Syncytiotrophoblast
Answer: A: Syncytiotrophoblast 
Explanation: Syncytiotrophoblast