Aspecies which is made up of different regional populations (subspecies that are physically distinguishable from each other) is said to be:
a. a polygenetic species
b. a polymorphic species
c. a polygonal species
d. a polytypic species
e. none of the above

d. a polytypic species

Explanation:

Under species comes a taxonomic rank called as subspecies. When a species can be divided into sub species it is called as polytypic species. A polytypic species has two or more than two sub species which are morphologically distinct from each other.

They generally live in different locations and are exposed to different environment thus look different from each other due to different adaptations. However they are still a part of same species so they can interbreed to produce fertile offspring. For example, leopard's scientific name is Panthera pardus and one of its subspecies is Panthera pardus fusca which represents Indian leopard.