need help explaining. will choose brainliest

Which of the following is not a random occurrence?

A selection of the best-suited traits for the environment, leading to adaptive evolution
Genetic drift changing the gene pool of a population and creating fluctuations in the allele frequencies
The bottleneck effect after an earthquake, resulting in a reduction of genetic variation
The founder effect, when a small population is isolated and the gene pool significantly reduced from the parent population

i chose A. Am i right or not? can pls help explain? tysm