In terms of natural selection, what is the best description of an organism that is fit?

Those organisms are fit which has the ability to survive in harsh climatic condition and transfer their traits to the next generation through the process of reproduction.

Explanation: Fit means they are strong and compete with other organisms for food, shelter and other survival items. Those organisms which are not fit could not survive in harsh environmental conditions and removed from that ecosystem.

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.

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