Final answer:
The salinity in water changes as you move from inland areas out towards the oceans; it increases gradually (Option B).
Step-by-step explanation:
As you move from inland areas towards the oceans, salinity in water increases gradually, resulting in brackish conditions in estuaries where freshwater and saltwater mix.
Freshwater sources like rivers typically have low salinity levels. As a river approaches an ocean, it mixes with the saltwater, creating an estuary where the water becomes brackish. The estuary is an area where saltwater from the ocean mixes with freshwater from inland sources, resulting in variable salinity levels due to factors such as the rate of freshwater flow and tidal movements. These tidal movements can bring high concentrations of saltwater into the estuary during high tides and reverse the current during low tides, thus making salinity levels fluctuate.
Thus, the correct option is B.