Final answer:
The reproductive tract prepares for the possibility of mating during the Proestrus phase, where follicles grow and the endometrium thickens in anticipation of ovulation and potential fertilization.
Step-by-step explanation:
The stage of the estrous cycle in which the reproductive tract prepares for the possibility of mating ("getting ready") is Proestrus (A). During this phase, the follicles on the surface of the ovary start growing in preparation for ovulation. Concurrently, the lining of the uterus, called the endometrium, starts to thicken.
This phase occurs before estrus, which is when the female is most receptive to mating. In contrast to species with an estrous cycle, humans experience a menstrual cycle, where a similar preparation phase is known as the follicular phase of the ovarian cycle, and is characterized by the thickening of the endometrium and the growth of the ovarian follicles.