C. Both.
Step-by-step explanation:
Changes that occur in different groups of organisms overtime that produce variations in a population relate to both macroevolution and microevolution. Although they are different, they both relate to this subject.
Macroevolution is on a big scale. This goes over organisms ancestors, large trends, and other groups of species that may be involved. This goes over a longer bit of time and is not as in depth.
Microevolution is on small scale. This goes over the different changes that may have occurred in allele frequencies from things like genetic drift, natural selection, or mutation. This goes in much more depth and looks deeper into what type of evolution may have happened.