This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrine System, Subject name: Physiology
The shoest hormone is: 
Select and explain. 
A. TRH, B. HCG, C. Insulin, D. Glucagon
A: TRH
Answer: A: TRH 
Explanation: Thyrotropin-releasing hormone is one of the smallest hormones in the body, consisting of a miniature chain of just three amino acid building blocks. It is made by a cluster of nerve cells in the hypothalamus, an area at the base of the brain just above the pituitary gland. This nerve cell cluster is known as the paraventricular nucleus. Longest hormone is HCG (250 amino acids)