[A]: In placental mammals, the placenta is connected to the embryo by the umbilical cord and has an essential role in the immu- nological protection of the embryo.
[R]: In mammals foetal components of titte placenta derive initially from the chondroblast connected with embryonic blood stream ei- ther through its contact with the yolk sac
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