In the placenta
A. Fetal and maternal blood mix freely in the sinusoids.
B. The PO2 in sinusoidal blood is similar to that in maternal arterial blood.
C. The barrier to oxygen diffusion is much greater than in alveoli.
D. Fetal blood in umbilical veins has a PO2 within 10 per cent of that in maternal sinusoids.
E. Fetal blood becomes more than 50 per cent saturated with oxygen.