Questions: What organ produces renin and what stimulates its release? - Kidney; high blood pressure - Adrenal glands; fight or flight situations (sympathetic response) - Thyroid gland; low blood oxygen levels - Kidney; low blood pressure

The answer is the fourth one: Kidney; low blood pressure.

Explanation for each option:

1. Kidney; high blood pressure - Incorrect. The kidney produces renin in response to low blood pressure, not high blood pressure.
2. Adrenal glands; fight or flight situations (sympathetic response) - Incorrect. The adrenal glands produce hormones like adrenaline and cortisol in response to stress, but they do not produce renin.
3. Thyroid gland; low blood oxygen levels - Incorrect. The thyroid gland produces hormones that regulate metabolism, but it does not produce renin.
4. Kidney; low blood pressure - Correct. The kidneys produce renin when they detect low blood pressure, which is part of the renin-angiotensin-aldosterone system (RAAS) that helps regulate blood pressure.

Summary: The kidney produces renin in response to low blood pressure.