This is regarding placenta origin. In kaplan blue book, bio question number 11 asks "whats involved in respiration and excretion and develops into placenta?", and the answer is allantois in the back of the book.
In cliffs, it says chorion is placenta and allantois is umbilical. Now although kaplan mentions allantois being umbilical cord in the answer section, it only adds "it will connect the fetus to the placenta".
The key word would be "excretion "in the question which only allantois is capable of, not chorion.
I think what I have stated is correct, but does anyone else have any additions that can clarify/affirm my thought process?