You are presented with the quiz "What happens when oxygenated blood doesn't reach the brain?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "arteries generally carry oxygen-rich blood" and "most strokes occur when a blood clot blocks an artery that carries oxygenated blood to the brain". 

So, what's the best answer to the question?


 

       a stroke    