Identify $A$ and $B$ and their respective functions:

• A
  $A \rightarrow$ Trophoblast,$B \rightarrow$ Inner cell mass,Function of $A \rightarrow$ Attach to the endometrium,$B \rightarrow$ Differentiated as embryo
• B
  $A \rightarrow$ Trophoblast,$B \rightarrow$ Inner cell mass,Function of $A \rightarrow$ Differentiated as embryo,$B \rightarrow$ Attach to the endometrium
• C
  $A \rightarrow$ Mesoderm,$B \rightarrow$ Inner cell mass,Function of $A \rightarrow$ Differentiated as embryo,$B \rightarrow$ Attach to the endometrium
• D
  $A \rightarrow$ Ectoderm,$B \rightarrow$ Mesoderm,Function of $A \rightarrow$ Attach to the endometrium,$B \rightarrow$ Differentiated as embryo