Answer- B. 3 hoursThe National Institute of Neurological Disorders and Stroke (NINDS) recombinant tPA (PA) Stroke Study showed a clear benefit for IV PA in selected patients with acute stroke.The NINDS study used IV PA (0.9 mg/kg to a 90-mg max; l0% as a bolus, then the remainder over 60 minutes) versus placebo in patients with ischemic stroke within 3 hours of onset.