Which of the following is a example of negative feedback?

a. the accumulation of blood platelets, which cause blood clotting, is triggered by a tear in the lining of the blood vessel.

b. the production of red blood cells, which transport oxygen, is triggered by a low level of oxygen in the blood.

c. during childbirth, the secretion of hormone oxytocin, which intensifies the contractions, is triggered by uterine contractions.