Solution: A breed is a collection of animals that are connected by descent and share several characteristics such as overall appearance, size, and traits. Leghorn, for example, is a better chicken breed. A race is a geographically isolated breeding population with a higher frequency of shared traits. Variety is a lower taxonomic rank than species or subspecies, however, it is used in the case of plants. A species is a collection of closely related creatures that are genetically similar and can usually interbreed.  

So, the correct option is (a).