Answer:
C. Allantois
Explanation:
The allantois is one of the four extraembryonic membranes that develop as an out-pocket of the yolk sac. The main function of allantois is to store the toxic waste, the nitrogenous waste and protects the embryo from the harmful effects of these waste products.
The allantois is a vascularized structure and its blood vessels become the blood vessels of the umbilical cord. Later, it becomes part of the urinary bladder.
