What is the purpose of blood spaces surrounding the villi ?

The correct option is C It provides space for air flow between the growing embryo and the mother

The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. The blood spaces, which surround the villi provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The developing embryo will also generate waste substances which can be removed by transferring them into the mother’s blood through the placenta.