[A] : Placenta is a tissue in eutherian mam- mals that has both embryonic and maternal tissue.
[R]: In mammals, foetal components of the placenta derive from trophoblast.
A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false