The amnion is an extraembryonic membrane that surrounds a developing embryo. It acts as a protective sac along with three other extraembryonic membranes: the chorion, the yolk sac, and the allantois. The membranes are then enclosed further by a shell (in birds, reptiles, and some mammals) or in a uterus (in most mammals). All four membranes protect the developing embryo through the provision of gas exchange, nutrient delivery, and waste excretion. The amnion is an extraembryonic membrane that surrounds an embryo. The membrane is not part of the embryo itself, but derives from tissues that emerged from the embryo. The amnion is made from two germ layers: the mesoderm and the ectoderm. The ectoderm forms the inner portion of the amnion, and a thin mesoderm layer connects the amnion to the chorion. Trophoblasts are cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta. Answer : (b)