Which Is Likely to Be the Most Critical Stage of Fetal

Which is likely to be the most critical stage of fetal development and why?

A) zygote, because most of the zygote is particularly vulnerable to teratogens
B) embryo, because most of the internal organs are formed during this period
C) fetus, because the fetus cannot survive outside the womb
D) infant, because the baby is finally exposed to environmental effects