Which of the Following Is the Most Likely Explanation for the Absence

Which of the following is the most likely explanation for the absence of a protective filter blocking the passage of alcohol between the maternal and foetal circulations in humans?

A) There has not been enough time to evolve such a barrier.
B) Such a barrier would probably also block important molecules that need to be passed to the foetus.
C) The maternal and foetal blood mix directly together in an area with many villi, so a barrier is impossible.
D) Alcohol has some positive effects on the foetus, so evolution has resulted in an intermediate level of filtering that blocks all but the worst abuses of alcohol.