In a Frog Embryo,gastrulation

In a frog embryo,gastrulation

A) produces a blastocoel displaced into the animal hemisphere.
B) occurs along the primitive streak in the animal hemisphere.
C) is impossible because of the large amount of yolk in the egg.
D) proceeds by invagination and involution as cells roll over the dorsal lip of the blastopore.
E) occurs within the inner cell mass that is embedded in the large amount of yolk.