Question

the densest water is..
more saline
deep er
colder
all of the above

Explanation:

Saline water has higher density due to dissolved salts. Deeper water is under pressure and colder (in many cases), and cold water is denser than warm water (for pure water, density is max at 4°C, but in ocean - colder water (below 4°C in some regions) is still denser than warmer surface water in other aspects like pressure and salinity gradients). So all these factors (more saline, deeper (which often implies colder and higher pressure - related density increase in some contexts), and colder) contribute to higher density.

Answer:

all of the above