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: Anatomy
True about morula: 
Select and explain. 
A. 8-cell stage, B. 16-cell stage, C. Solid mass with fluid inside, D. Ach. Barrier present
B: 16-cell stage
Answer: B: 16-cell stage 
Explanation: B. i.e. 16 cell stage