All of the following are possible EXCEPT
a. an involuntary increase in the rate of breathing.
b. a voluntary increase in the rate of breathing.
c. inhibition of the respiratory centers in the brain.
d. a voluntary decrease in the rate of breathing.
e. voluntarily holding one's breath until death occurs.

All of the following are possible EXCEPT

a voluntary decrease in the rate of breathing.

Explanation:

A voluntary does not decrease in the rate of breathing

it is either c or d and i know for sure it is not a or b

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.