You are presented with the quiz "corals use what to communicate with each other" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "echinoderms use pheromones to communicate with each other" and "ascothoracican barnacles attach to echinoderms or corals". 

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


 

  pheromones         