(a) Stabilizing selection, also known as negative or purifying selection, is a sort of natural selection in which the population mean stabilizes on a non-extreme trait value. This is a typical and important stage in the process because most features do not arise owing to abrupt changes in time. For instance, any human's birth weight. It's the incorrect response.
(b) In population genetics, directional selection is the mechanism of natural selection in which one extreme phenotype is favored over other phenotypes, resulting in a shift in allele frequency in the direction over time. It's the incorrect response.
(d) Frequency-based selection is an evolutionary process as well. In this process, the fitness of each phenotype is determined by its frequency in comparison to other phenotypes in a population. Positive frequency dependent selection is becoming more widespread, and it improves phenotype fitness. It's the incorrect response.