A.Salinity
The deeper you make your way the hotter it gets because it is getting closer to the inner core which is 4000-4700 Degrees Celsius so that definitely would not be the answer. It also gets more and more dense and the pressure changes and you can see this by the fact that some mantles are liquid but because of the pressure it forces it into a solid. Sorry for the terrible explanation, I am bad at explaining things. Hope this helps!
