I can't see any diagram but the correct statement should be:
"Salinity decreases because the stream adds freshwater to the ocean"
The other statements are false.
F Salinity increases because the stream adds salt to the ocean
T Salinity decreases because the stream adds freshwater to the ocean
F Salinity increases because the stream adds freshwater to the ocean
F Salinity remains the same because the steam adds freshwater to the ocean