Lack of menstruation is caused due to

The main function of mammalian corpus luteum is to produce

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.

Assertion $A$: Endometrium is necessary for implantation of blastocyst.

Reason $R$: In the absence of fertilization, the corpus luteum degenerates that causes disintegration of endometrium.

In the light of the above statements, choose the correct answer from the options given below:

Given below is a flow chart showing ovarian changes during menstrual cycle. Fill in the spaces giving the name of the hormones responsible for the events shown.

$\boxed{\rm {Primary follicles}}$

$\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \downarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \leftarrow \,\boxed A$

$\boxed{\rm {Graafian follicle}}$

$\,\,\,\,\,\,\,\,\,\,\,\,\,\, \downarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \leftarrow \,\boxed B$

$\,\,\,\,\,\,\,\,\,\,\,\boxed{\rm {Ovum}}$

$\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \downarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \leftarrow \,\boxed C$

$\boxed{\rm {Corpus leuteum}}$

What are the changes in the oogonia during the transition of a primary follicle to Graafian follicle ?