I looked it up and it should be D. Nerve cells :)
Answer:
The correct answer would be zygote...blastocyst...embryo...fetus.
The fertilization of sperm and egg results in the formation of zygote. It receives genetic material from a male as well as a female parent.
It divides with the help of mitotic divisions and results in the formation of 2, 4, 8, and 16 celled stages.
It results in the formation of the hollow spherical ball of cells termed as a blastocyst. The cells are distributed to form the outer layer termed trophoblast and inner cell mass which gives rise to the embryo.
Trophoblast help in the implantation of the blastocyst into the uterine wall.
The cells of the embryo undergo organogenesis during different organs such as heart, brain, lungs et cetera are formed.
In humans, almost 9 weeks after the fertilization the developing embryo is considered a fetus.
The fetus development continues until birth.
