What must be true for natural selection to happen?
A. there must be no predators in the ecosystem.
B. Resources must be limited in the ecosystem.
C. there can be no competition for resources.
D. The population must be bellow carrying capacity.

B.

Explanation: There must be competition for resources.

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 : )