Answer: The correct option is B (progesterone).
Step-by-step explanation:
The cervix is the ring of muscles also called the neck of the uterus in female reproductive system. This protrudes through the anterior wall of the vagina, opening into it at the external os.
After the fertilization of the ovum by the spermatozoa, the uterus prepares for the implantation which results from the secretion of hormones. Under the influence of oetrogen, secreted by the developing follicle, the cells of the endometrium divide rapidly causing the endometrium to build up and thicken.
While the viscosity of cervical mucus changes in response to hormone levels and during pregnancy, progesterone fosters the production of highly viscous mucus resulting in the formation of a plug that forms a physical barrier to bacteria and prevents their ascension into the uterine cavity. This plug is called CERVICAL PLUG.