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: Physiology
Beta HCG is secreted by ? 
Select and explain. 
A. Ovary, B. Pituitary, C. Corpus luteum, D. Placenta
D: Placenta
Answer: D: Placenta 
Explanation: Ans. is 'd' i.e., Placenta