The correct option is C Reproductive success
The term natural selection was coined by Darwin. It describes the process by which the organisms with favourable variations survive and reproduce at a higher rate because they are the fittest to face their surroundings. The features of Darwin’s natural selection process are overproduction, struggle for existence, variation, survival of fittest, natural selection and origin of new species.
Overproduction leads to the scarcity of resources in an expanding population which results in competition between individuals of the same species and others for basic necessities like space, shelter and food. This is called the struggle for existence. This is one reason for natural selection. Only those organisms which have favourable variations are selected by nature. They are the fittest organisms for survival.
The fitness, according to Darwin, refers ultimately and only to reproductive fitness. Thus, Darwin concluded that reproductive success or reproductive fitness is the best concluding explanation of natural selection.
Use and disuse of organs is one of the basic concepts of Lamarckism. According to Lamarck, if an organ is constantly used, it would be developed better whereas a disused organ results in its degeneration.
So, the accurate answer is option c.