Which of the following describes a positive feedback loop? O When blood sugar concentration is too low, the endocrine system secretes hormones that increase blood sugar concentration to a normal level.
O When the body senses that the heart rate is very high, it secretes hormones that decrease the heart rate.
O When blood sugar concentration is too high, the endocrine system secretes hormones that decrease blood sugar concentration to a normal level.
O When someone is exercising intensely, the body secretes hormones that increase oxygen supply for cellular respiration.​