Gastrulation
a. changes the hollow blastocyst into a hollow embryo that has three tissue layers
b. changes the solid blastocyst into a hollow embryo that has three tissue layers
c. changes a gastrula into a blastocyst
d. changes a hollow embryo into a solid gastrula
e. stimulates labor

The appropriate response is A. Gastrulation is a stage ahead of schedule in the embryonic improvement of most creatures amid which the single-layered blastula is rearranged into a trilaminate (three-layered) structure known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm.