The correct option is D Microevolution
Microevolution is also called as sequential evolution, which involves a continuous and gradual change in an interbreeding population, usually giving rise to new subspecies and geographical races. Basic process involves changes in gene frequencies in a population from one generation to the next. Microevolution is produced by stabilizing or normalizing natural selections that operate in stable environmental conditions and in short time span. So, the accumulation of small changes in the gene pool over a relatively short period of two or more generations is called microevolution. Thus, option B is correct.
Macroevolution is also called as adaptive radiation, which includes evolutionary changes above the species level that may result in the production of new adaptive types through genetic divergence.
Megaevolution includes formation of new groups, classes or phyla due to evolution of new types from its predecessors by general adaptation.
Quantum evolution is the comparatively rapid transition from one stable type of biological adaptation to another distinctly different type under the influence of some strong selection pressure.