Give scientific reasons: Pills taken orally prevent pregnancy.

(N/A) Oral contraceptive pills contain a synthetic combination of progesterone and estrogen hormones.
These pills are typically taken starting from the $5^{th}$ day of the menstrual cycle.
The primary mechanism of action is the inhibition of ovulation by suppressing the release of follicle-stimulating hormone $(FSH)$ and luteinizing hormone $(LH)$ from the pituitary gland.
Additionally,these hormones alter the quality of the cervical mucus,making it thick and viscous,which prevents the entry of sperm into the uterus.
Furthermore,they alter the lining of the endometrium,making it unsuitable for implantation.
By preventing ovulation and blocking sperm entry,these pills effectively obstruct the process of fertilization,thereby preventing pregnancy.