The respiratory function of the embryo is performed by

The brain and spinal cord are derived from which germ layer?

Match the items $A, B, C, D$ of table $'A'$ with the items in table $'B'$. Then,the correct pairing sequence of $A, B, C, D$ will be:
Table $'A'$ | Table $'B'$
$A.$ Cleavage | $1.$ Formation of $3$ germ layers
$B.$ Gastrulation | $2.$ Formation of embryo spinal cord
$C.$ Neurulation | $3.$ Results in formation of skeleton and muscles from mesoderm
$D.$ Organogenesis | $4.$ Pattern depends on the amount and distribution of yolk

Match List-$I$ with List-$II$ related to embryonic development at various months of pregnancy:

List-$I$	List-$II$
$A$. The foetus movement starts and hair appears on the head	$I$. $24$ weeks of pregnancy
$B$. The foetus develops limbs and digits	$II$. $20$ weeks of pregnancy
$C$. The foetus develops external genital organs	$III$. $8$ weeks of pregnancy
$D$. The foetus body is covered with fine hair; eyelids separate and eyelashes are formed	$IV$. $12$ weeks of pregnancy

Choose the correct answer from the options given below:

The gestation period of elephants is about

At which stage of embryonic development is cell differentiation observed?