During the blastocyst stage of embryonic development, the embryo is organized into three germ layers: endoderm, mesoderm, and ectoderm. How does each germ layer develop as the embryo grows?
a. Each germ layer produces specific body tissues and organs.
b. The three germ layers fuse together, and the united germ layers produce all body tissues and organs.
c. The endoderm and ectoderm are shed, and the mesoderm produces all body tissues and organs.
d. The mesoderm provides nutrients for the embryo, and the endoderm and ectoderm produce all body tissues and organs.