After future divisions, what becomes a solid ball? What is it called? Define blastulation and what causes it to occur? By which day has it become this structure?
a) Blastomere; zygote; formation of blastocyst; fertilization; day 5
b) Morula; blastocyst; formation of blastula; implantation; day 3
c) Blastula; morula; formation of blastocyst; implantation; day 5
d) Morula; blastula; formation of blastocyst; fertilization; day 3