This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
All of the following have receptors which are transcription factors except 
Select and explain. 
A. Insulin, B. Estrogen, C. Vitamin D, D. Glucocorticoid
A: Insulin
Answer: A: Insulin 
Explanation: None