Final answer:
Cold, saline water is the most dense, with maximum density occurring at around 4°C. Salt increases water's density and cold water (near 4°C) is denser than warm water, making answer a (Salinity, cold water) correct.
Step-by-step explanation:
The density of water varies based on both temperature and salinity. Answering the question of which type of water is most dense involves understanding how these factors influence water's density. Cold water with salinity is indeed more dense than warm water, and water's density is highest at around 4°C. When water is colder than this point, it begins to expand and thus becomes less dense, which is why ice floats on top of water.
Water at the bottom of lakes or oceans tends to be around 4°C because this is where it is most dense, and therefore, it sinks below less dense water. Additionally, salt increases the density of water. Therefore, combining both factors - low temperature (close to 4°C) and the presence of salt - yields the most dense form of water.