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: Ophthalmology
Which is the shoest acting mydriatic? 
Select and explain. 
A. Tropicamide, B. Atropine, C. Phenylephrine, D. Hyoscine
A: Tropicamide
Answer: A: Tropicamide 
Explanation: Tropicamide is the quickest (20-40min) and shoest acting (3-6hours) mydriatic. Atropine is a potent mydriatic but its slow and has long lasting action. With it, pupil dilates in 30-40min but cycloplegia takes 1-3hours.