Answer:
The correct answer is option D. "variation".
Step-by-step explanation:
Variation is a term used to describe the phenotype differences among individuals of the same species, such as the differences among the different breeds of dogs. There are two types of variation, inherited and environmental variation. The first one results from the different genes in the offspring that are passed from the parents, and environmental variation results from the exposure of different conditions in the surroundings where individuals live.