The thymus gland secretes hormones called:

This is because it is an example of a positive feedback loop, which amplifies the change and moves the system away from its normal state.
A negative feedback loop is a mechanism that reverses a deviation from the set point and maintains homeostasis.
Choice A is wrong because increasing heart rate and force of contraction when blood pressure falls is a negative feedback loop that restores blood pressure to normal.
Choice B is wrong because secreting insulin after a meal to return blood sugar concentration toward normal is a negative feedback loop that regulates glucose levels.
Choice D is wrong because shivering when body temperature falls below normal is a negative feedback loop that increases heat production and raises body temperature.
Normal ranges for blood pressure are 90/60 mmHg to 120/80 mmHg, for blood glucose, are 70 mg/dL to 140 mg/dL, and for body temperature are 36.5°C to 37.5°C or 97.7°F to 99.5°F.

The thymus gland is an essential part of the immune system that produces and matures T cells, a type of white blood cell that defends the body from infections.
Thymosins also regulate immune cell production and inhibit aging.
Choice A is wrong because thyroxines are hormones produced by the thyroid gland, not the thymus gland.
Thyroxines control metabolism and affect growth and development.
Choice B is wrong because melatonins are hormones produced by the pineal gland, not the thymus gland.
Melatonins control circadian rhythms and sleep cycles.
Choice D is wrong because prostaglandins are not hormones, but lipid compounds that have hormone-like effects.
Prostaglandins control inflammation, blood pressure, muscle contraction, and other functions.