Final answer:
Ocean salinity is highest where evaporation rates are high and precipitation is low, as evaporation leaves salts behind while precipitation dilutes them.
Step-by-step explanation:
Salinity in the ocean is highest in regions where evaporation is high and precipitation is low. The reason for this is quite straightforward: evaporation removes water from the ocean, leaving salts behind and thus increasing the salinity of the remaining water. In contrast, precipitation adds fresh water to the ocean, diluting the salt and decreasing salinity.
Evaporation is a distillation process that produces nearly pure water, leaving the dissolved ions behind in the ocean, which increases the salinity. An area with high evaporation rates, particularly in regions with warm temperatures, will have less water to dilute the salts. Conversely, regions with high precipitation receive more fresh water, which mixes with seawater and reduces its salinity.
Therefore, the correct answer to the question is 'evaporation; precipitation'.