You are presented with the quiz "How is survival ensured around hydrothermal vents?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "organisms cluster around hydrothermal vents in the ocean floor" and "to survive, some organisms living near hydrothermal vents have formed close associations". 

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


 

      Being in a cluster     