Which part of the embryo is responsible for its implantation in the uterus?

In teleosts,reptiles,and birds,the cleavage pattern is:

In the blastocyst,the blastomeres are arranged into an outer layer called _ $A$ _ and an inner group of cells attached to the trophoblast,called _ $B$ _.

Which one of the following is the most likely root cause why menstruation is not taking place in a regularly cycling human female?

Following are some events occurring during the fertilization process. Arrange the $CORRECT$ sequence of events and choose the option given below.
$i$. Fertilizin-antifertilizin reaction.
$ii$. Cortical reaction.
$iii$. Acrosome reaction.
$iv$. Karyogamy.
$v$. Capacitation of sperms.

$A$ layer of cortical granules is found beneath the