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
Among the following longest acting ocular beta-blocker is: 
Select and explain. 
A. Betaxolol., B. Timolol., C. Cartiolol., D. Metoprolol.
A: Betaxolol.
Answer: A: Betaxolol. 
Explanation: Betaxolol is a cardioselective beta-blocker which can be used for the treatment of glaucoma.