The first event to occur when an adequate stimulus is applied to a neuron is

i might be wrong but i think its a. let me know if i’m right and have a good rest of your day!

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

i hope this : )