Concept:The placenta lets useful substances pass from mother to foetus, but waste gases pass in the reverse direction.
Explanation:Glucose passes from the mother’s blood into the foetal blood as a nutrient.
Antibodies also cross the placenta, giving the foetus passive immunity.
Some viruses can cross the placenta and infect the foetus.
Carbon dioxide is a waste gas produced by the foetus.
It moves from foetal blood into the mother’s blood to be removed.
Therefore, carbon dioxide is not transferred from the mother’s blood into the foetus.
Answer:A. carbon dioxide