Answer:
Option). oxygenated and deoxygenated blood mix due to the ductus arteriosus.
Step-by-step explanation:
Fetal blood circulation is different from adults as in fetus, oxygenated and de-oxygenated blood get mixed due to the ductus arteriosus.
It is because the oxygenated blood from the placenta enters to the right atrium of embryo through caudal vena cava, while de-oxygenated blood that returns from the embryo head also enters to its right atrium through cranial vena cava.
The oxygenated blood from right atrium enters to the left atrium and then to the left ventricle, from where it gets pumped to the body. The de-oxygenated blood from right atrium is pumped to right ventricle and travels to the aorta through the ductus arteriosus, where it is mixed with oxygenated blood.
Thus, the correct answer is third option.