Structure A is used for (4) cell communication. The cell membrance has receptros for cell communcation.
Structure B is used to (1) extract energy from nutrients. The mitochondria is the power house of the cell.
Structure C is used for (1) protein synthesis. The golgi apparatus is where protein is created.
Ocean waters has its own level of density which depends of the climate, temperature and most of all the location where it came from. The more the ocean water absorbs heat the more its density as a result it rises above from cold to hot. So the the water from the Antarctica usually is less dense and then become more dense when it goes to the equator which is more hot.
On edge the answer is similar size, mass, and density.
