The correct option is A Archenteron
During gastrulation, an embryo's developing digestive tube initially forms as a blind pouch called the archenteron which becomes the gut in the later stages of life. In protostome development, the solid masses of mesoderm splits and form the coelom. In contrast, in deuterostome development, the mesoderm buds form the wall of the archenteron and its cavity becomes the coelom. Thus the correct answer is option B.