During gastrulation,a cavity is formed and is found in the mature gastrula. What is it called?

$A$ : The morula passes through the phase of compaction,producing two major types of cells: the peripheral cells and the inner cell mass.
$R$ : The descendants of the inner cell mass become the trophoblast cells.

Match the columns:

Column $I$	Column $II$
$(a)$ Third week	$(1)$ Development of pre-umbilical cord
$(b)$ Third month	$(2)$ Body develops but head remains big
$(c)$ Fourth week	$(3)$ Embryonic slit widens
$(d)$ Fourth month	$(4)$ Muscles activate

Which of the following structures forms the birth canal after fertilization?

Which of the following embryos exhibits a parasitic mode of nutrition?

Foetal membranes provide