The theory of natural selection was first expounded by Charles Darwin and today it is believed to be the main process that brings about evolution.
This process is defined as the process whereby organisms who better adapt to their environment tend to survive and produce more offspring.
Hence, according to this statement, option C is correct.
More organisms are born than can survive.
Sexually - better adapt
Reproducing sexually allows for gene variation which helps in changing environments. Asexually would be the same genetically and it would be difficult to adapt
A couple of reasons why the black mice changed after the eruption of the volcano are because the black mice blended in with the surrounding better. This helped them to survive and to reproduce. Also, since they were black in color, the predators were unable to see them because of the environment color change.