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
Embryo proper is derived from which pa of morula: 
Select and explain. 
A. Inner cell mass, B. Outer cell mass, C. Both of the above, D. None of the above
A: Inner cell mass
Answer: A: Inner cell mass 
Explanation: Approximately 3 days after feilization, cells of the compacted embryo divide again to form a 16-cell morula (mulberry). Inner cells of the morula constitute the inner cell mass, and surrounding cells compose the outer cell mass. The inner cell mass gives rise to tissues of the embryo proper, and the outer cell mass forms the trophoblast, which later contributes to the placenta. Ref: Langman's embryology 11th edition Chapter 3.