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
Which of the hormone has 4 subunits and 2 units for tyrosine kinase receptor binding? 
Select and explain. 
A. Insulin, B. Glucagon, C. T3, D. ADH
A: Insulin
Answer: A: Insulin 
Explanation: Insulin receptor is 'enzyme linked receptor Insulin binds to alpha-subunits => due to linkage, poions of b-subunits become auto-phosphorylated