Corpus luteum is formed in

Which phase of the menstrual cycle in humans lasts for $7-8$ days?

Given below is a flow chart showing ovarian changes during the menstrual cycle. Fill in the spaces by providing the names of the hormones responsible for the events shown.
$\boxed{\text{Primary follicles}}$
$\downarrow \leftarrow \boxed{A}$
$\boxed{\text{Graafian follicle}}$
$\downarrow \leftarrow \boxed{B}$
$\boxed{\text{Ovum}}$
$\downarrow \leftarrow \boxed{C}$
$\boxed{\text{Corpus luteum}}$

What is the result of a decrease in the level of progesterone?

What is the cause of menstruation?

The menstrual cycle occurs in: