You are presented with the quiz "objects will sink between boundaries with different what due to gravity" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "if an object in a fluid is more dense than that fluid then that object will sink in that fluid because of gravity" and "waves can be created at the boundary between fluids of different densities". 

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


 

   densities        