Answer:
The result which could confirm that natural selection is a process that can drive evolution is "change in the allele frequency of the population".
When salinity of the river is increased, the individuals which can tolerate the changing environment would survive.
Due to natural selection, these individuals would survive and reproduce more efficiently as compared to the individuals which lack such traits or adaptations.
Over generations, the population would only consist of these organisms and thus, the allele frequency of the population would change.
Hence, the population would evolve.
