A closed system is a system in which (a) Matter can enter and leave
(b) Matter can enter but cannot leave
(c) Matter can leave but cannot enter
(d) Matter does not enter or leave

B - Matter can enter but cannot leave

Explanation:

I looked it up, sorry if wrong

"menstrual cycle is a complex cycle that consists of several processes. order of occurrence of steps in menstrual cycle are as follows:

1. high progesterone levels maintain the endometrium lining of the uterus.

2. endometrium lining breaks down and low levels of estrogen stimulate the pituitary to release fsh and lh.

3. fsh and lh stimulates the follicles to develop and the oocyte to produce estrogen.

4. rising estrogen levels suppress fsh production and development of other follicles.

5. a spike in lh causes follicle to rupture.

6. a breakdown of corpus luteum causes progesterone level to drop."