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: Anatomy
Location of carotid sinus is: 
Select and explain. 
A. At the termination of CCA, B. Behind the bifurcation of CCA, C. At the beginning of ICA, D. Both 1 and 3
D: Both 1 and 3
Answer: D: Both 1 and 3 
Explanation: Carotid sinus:

It is a fusiform dilatation at the terminal end of common carotid artery or at the beginning of internal carotid artery. 
It has rich innervation from glossopharyngeal, vagus, and sympathetic nerves. 
The carotid sinus acts as a baroreceptor (pressure receptor) and regulates the blood pressure in the cerebral arteries.

Key Concept:
Carotid sinus is a fusiform dilatation at the terminal end of common carotid artery or at the beginning of internal carotid artery.