Which process is necessary for the development of an embryo from a zygote?

If both ovaries are removed from a pregnant human female in the first trimester of pregnancy,then it will lead to:

With respect to derivatives of germinal layers in human beings, complete the analogy.
$Ectoderm : \text{Sweat glands} :: Endoderm :$ . . . . . . .

The blood flowing in the umbilical cord is:

Major features of embryonic development at various months of pregnancy are given below. Choose the correct option for the correct sequential events.
$(i)$ The first movements of the foetus
$(II)$ The foetus develops limbs and digits
$(III)$ The embryo's heart is formed
$(IV)$ The body is covered with fine hairs

Foetal sex can be determined by examining cells from amniotic fluid by looking for: