Answer:
The correct answer would be A) genetic drift happens by chance.
Both natural selection and genetic drifts are the natural phenomena by which evolution takes place, however, they differ in a way that genetic drift happens by chance whereas natural selection happens as a result of differential reproduction success.
Natural selection is the process by which organisms with better adaptation for changing environment have better chances of survival and reproduction.
In contrast, in genetic drift, variation in genotype frequencies of a population takes place as a result of random chance. For example, individuals with a particular gene die or are not able to reproduce.