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
A teenager has seen her local physician complaining of persistent and severe headaches. Her physician diagnosed migraine and prescribes sumatriptan, which acts by which of the following mechanisms? 
Select and explain. 
A. Dopamine 1 agonist, B. GABAB antagonist, C. Muscarinic 3 antagonist, D. Serotonin 1D agonist
D: Serotonin 1D agonist
Answer: D: Serotonin 1D agonist 
Explanation: Sumatriptan is a serotonin 1D agonist that is used to abo migraine headaches. It is also effective in the treatment of cluster headaches. Currently, no dopamine 1 (D1) agonists, GABAB antagonists, or muscarinic m3 (M3) antagonists are used clinically.