What is the specific function for the substance contained in letter E?

Identify the extraembryonic membrane at “B”.

Properly identify the stage labeled  “E”

Name the cell indicated by “D” 

Properly identify the stage labeled  “K”

Identify the structure indicated by “C” 

Identify the embryonic germ layer (green) at “B”.  

Identify the structure (red) at “A”.

Does the area at “A” contain maternal or fetal blood?  

Identify the structure at “B”.