B. Salinity of sea water is more than that of river water
C. Sea water is still while river water is running
D. Density of sea water is more than that of river
Explanation
Due to high salt in the sea water the density of the seawater is higher as compared to river water. So as the density increases the buoyant force also increases.
It is easier to swim in sea water than in river water because we observe more buoyant force in sea water due to its hardness than in river water.
