This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
IV thrombolysis is of no use in ischaemic stroke beyond 
Select and explain. 
A. 6 hours, B. 12 hours, C. 18 hours, D. 24 hours
A: 6 hours
Answer: A: 6 hours 
Explanation: In IV PA trails, efficacy was confirmed in the <3-h time window, and efficacy likely extended to 4.5 h and possibly to 6 h.Depending on the country, IV PA is approved for up to 4.5 hCriteria for administration of Intravenous Recombinant Tissue Plasminogen Activator (PA ) for Acute Ischemic Stroke (AIS)Clinical diagnosis of strokeOnset of symptoms to time of drug administration <=4.5 hCT scan showing no haemorrhage or edema of >1/3 of the MCA territoryAge 18 >= yearsConsent by patient or surrogateRef: Harrison 19e pg: 2562